Doesn't matter how educated or uneducated they are, the brainwashing starts at the cradle with your parents and continues ad infinitum with society, peers, media, etcetera. It only takes a moment of clarity and courage to eschew that shit.

As for me, I started out as a theist, being raised and brainwashed by theists. In my late 20's I dared to do research on religion, and discovered that it is a scam (they always ask for money) based on nothing but mythology. I have my public schooling to thank for teaching me to think scientifically. Otherwise, I would still be deluded by the more lazy side, which tells you not to think too much, but just accept, on blind faith, whatever the church leaders tell you. THANK YOU, public schools, for giving me the tools to free myself from such a horrible scam.

I liken it to language. Whatever your family speaks the children will speak.
My family speaks atheists

IMHO, atheists and agnostics seem to be more educated than their theist counterparts.

Educated in what?

Some theists have a great deal of education in the faux discipline of theology. That does not bestow explanatory or predictive power concerning lived experience. It is just self-referential, self-ratifying nonsense basically. That's not to say it isn't elaborate or something you couldn't occupy yourself with for a lifetime. Or even to say it has zero value (you would need a good grasp of comparative theology to understand the meaning of many ancient writings and cultural practices, etc).

When it comes down to your average Joe Pew-Warmer, theism is just a learned coping mechanism, culturally transmitted, and adhered to out of comfort -- in part because it provides easy community and a sense of belonging, and for those who like it, tradition and ritual. It is something to anchor oneself to. It isn't necessary for it to be true for that anchoring to happen. Joe isn't encouraged to think much about it. Or at least not to think critically about it. To him, it just is.

That's not to say some people don't put more thought and self-awareness than that into it; it's just to say thought is strictly optional, and in terms of strengthening a theistic outlook, is more of a bug than a feature. Our brains have evolved with a ton of confirmation bias and agency inference and other sloppy processes that are breezily unconcerned with relationship to fact; it's mainly concerned with relation to feeling and intuition.

If a person is willing to do the work on the research to discover that all religions are a sham, created by humans to control other humans, in these instances the person will not be religious at all. Most people are not willing to do that sort of work so it is just easier to believe whatever bullocks they are fed.

I never made any decision about my theistic views...I was never convinced that god existed so it began and ended there.

Most people don't have a clue about theistic and religious differences and simply make up their minds from words of others, doing this without any study at all. Some atheists just dismiss the whole idea without looking into it. People decide what they believe in mostly on what their parents believed in, and they only change their beliefs as they get older and look at things more closely. It is not a matter of which religion is the right one out of a whole world of religions. It is a matter of why any religion would be the right religion. There is also the question of why would you need a religion?

If Jesus died for your sins why do you have to repent? If god cannot stand sin of any kind why is Jesus sitting at his right hand in heaven? I ask this because all the sins of the world were put on Jesus. Where did those sins go?

You can't decide what to believe. Religious people are indoctrinated from birth until they are old enough to think for themselves. By that time most of them have been convinced that their parents religion is true. Unless they go searching for evidence to either back up their beliefs or contradict them, they will be stuck there. You believe what you are convinced is true. You don't just decide to believe something.

I learned those definitions only after I left and learned what faith really is. When all your family and friends are true believers it's difficult for most to break free.

I did not "decide" my theistic beliefs. I was raised to believe certain things and I accepted what I was taught. Burning questions caused me to learn more about the Bible; and this research led me to no longer accept it as the word of any god. This caused me to reject what I had been taught about god, but it did not cause me to stop believing in one--of some kind.

I did not decide to become an atheist. It was a natural consequence of learning more science. I came to realize that there is no evidence for any kind of god and no need to insert one, of any kind, in order to explain how the universe works. So, why insert one?

I am an agnostic atheist: I accept that it simply cannot be known/proven whether or not some kind of god being or universal consciousness exists; but I have no reason to believe that one does, or might, exist.

I think the answers to this will be as varied as each individual. In my humble opinion I believe that that average theistic person is lead that way by others searching for meaning or an explanation of why events occur. They don't look hard enough and find a faith based solution that placate their need to understand.

Of these there are those who study and aren't placated by a simpler explanation and thus search for a scientific explanation. Yet they are comforted by the idea that a higher form cares about them. Or they hope for something after the life we're in.

As an Atheist, I realized I don't buy into a higher form, that their are scientific reasons for events, and that death is "game over" no respawn; though I woudn't mind being wrong and on getting a chance to come back. One of these days I will find out, but will I actually know?

I go through these phases too, where I try to decipher the why's and how's of our messed up species.
I still don't really get it. I grew up going to a private, Christian school...Church of Christ, no less! And even back then, I was critical of all I'd been told. My parents were believers, but we had a houseful of encyclopedias and books and programs like National Geographic were always on the TV. Hell, I can't remember when there weren't National Geographic, Time and Popular Science magazines in bathroom.
At one point I remember trying real hard to resolve it all into a neat bundle. Maybe there really was a big bang, it's just that God made it. Maybe there really were Neanderthal people, maybe Adam was a Neanderthal....I mean, as a little kid, I tried very hard to have it all make sense!
However, as we all know, it certainly does not make sense. No sense at all.
I can only attribute blind faith to fear and willful ignorance. I don't know how to get past it.

My experience is: most people don't know what those words mean.

There is a difference between being educated and being able to think.

The word "belief" is ambiguous. The God Mob exploit this ambiguity to their own ends.

My own usage of the word belief is "acceptance of a claim that is made without any supporting evidence". As such, I have no beliefs. (Hint: my world view is entirely evidence-based.) My world view can and does change in the light of new information.

To answer your first question, there are some people who have a very clear understanding of the differences between theism, agnosticism and atheism, and there are other people who have an extremely poor understanding of those differences. The latter group of people are typified by having little or no ability to think analytically.

Usually starts with family

I would say it's heavily determined by the environment people are born into. In some countries, your religion is chosen for you. Even when it's not, it effectively is through social pressures to conform.

As for what causes people to change their beliefs, if it ever happens, it's down to the compatibility of a competing religion and the theists desires.

Many have converted to radical islam, for example, out if a desire to fill what they are led to believe are their Gods' wishes. But the fact that it often happens in young people shows that much of it may be done out of a desire to belong.

Contrary to the common belief..... Education and Reason, Education and Wisdom have NO correlation. I am a living example.

Educated people use logic with all parts of their life, except when it comes to religion. Most theist don't understand what agnosticism and atheism is. They don't research anything when it comes to religion, they use faith. You can't make a person give up religion, they have to do that on their own time.

Aaaw! It's so sweet you think people decide rationally what to believe about deities, or even wonder about the different word meanings, or care.
Parents and local society shape children's religious beliefs from earliest years. Young children mostly accept parental teachings as true, the same as they believe what parents say about the sun rising each morning.

If anyone was to actually read, & think while reading, the Babble, that should be enough to raise Major questions!

Most would not.

Wonder why they would care. I am sure beliefs aren’t an intellectual decision.

Being a part of a group is a different matter

Boy there is alot to unpack here.

How educated are people when it comes to deciding their theistic beliefs?
The key here is that it is an UNeducated decision. Religion releys on ingnorance. If knowledge was a factor there would be no religion.
Most do not "decide" on their religion. It us usually imposded on people from childhood by their family and culture.

Do you feel most people understand the difference between theism, agnosticism, and atheism?
No this site is a great example of there being debate even among the community. Many believe due to their misguided religious teachings that atheist are Satanist or are simply rebelling god and are incapable of not believing. Though more are beginning to understand at least somewhat. I would say that many or atmleast half of Americans understand. I am not speaking of other countrys.

On what basis, work and research do people decide which they believe in?
It simply does not work that way. Christopher Hitchens one said "Atheism is not choosen, it is discovered". Try to believe that Scooby Doo is a real living talking dog right now. You can pretend but you really can't without somthing to base that understanding on. We have to somehow confirm something to be real or true before we can believe, we can not decide. How our minds unconciously make those choices is not something we can control.
Usually some sort of evidence that we can observe is what we base our reality on. I know that is kinda vague but our brains are compleex and there is no one or certain combination of things that make us determine reality. I like to look at what is factual and not to determine what is real.

What if anything, causes people to change these beliefs?
It can be a great variety of things. Corruption in the church, a lack of evidence, holy books being contradictory, theist doing evil deeds, things being obviois fiction etc.
When there is evidence that for example religion is not all good (such as a beheading) it causes cognative dissodence. If people are concerned about what is real more than just wanting to believe they usually investigate or question their beliefs. If beliefs do not align with reality they CAN NOT believe the lie. Though some continue to lie to themselves and others that they believe.

The only beliefs worth having are those that you work out for yourself . So the best education for changing beliefs is to mentally " walk alongside" other people as they relate their belief journey. So it might be a good idea to work out some sort of 'pilgrimage' . For those who have access to The UK could I suggest ' Down House ' near Biggin Hill. They run Air shows at Biggin Hill and that may help you get there but the house is famous as Charles Darwin's family Home . It has lots to see.