What is it called when you are able to choose who you worship?

Being able to choose what or whom you worship is called freedom of religion.

An atheist is a person who doesn't believe in God or religion, and that is a choice also. Atheists usually believe in the scientific origin of life rather than creation by God. In free countries that are not controlled by one particular religious group, most people, once they grow up, are able to choose who they want to and will worship. For example, if you grew up Catholic, once you were legally of adult age and understood religion more, you could convert to being a Protestant or join some other religion.