Believers, put yourself in my place.

[Huggy Bear]

Let's say I don't believe in dragons.

Then suddenly, I see a load of dragons. Obviously, I "change" my belief. But it wasn't a conscious choice. It was inevitable, given the new information.

I can't sit here right now and suddenly choose to believe in dragons. If I could do that, I'm some kind of mental person.

I have the ability to have my mind changed. Of course I do. That's just stating an obvious fact. It doesn't make belief a choice.

I don't know why this is so hard for you to understand,  a "belief" is accepting that something is true without proof.

https://en.oxforddictionaries.com/definition/belief

belief

1. An acceptance that something exists or is true, especially one without proof:

     1.1 Something one accepts as true or real; a firmly held opinion:

So by definition what you describe is not changing a belief.

In your example, seeing a load of dragons would be PROOF, thereby making dragons an actual fact and no longer a belief...

Your belief that a God doesn't exist isn't based on any evidence, if it is, then provide it.