sometimes changing from one orientation to the other happens naturally
As in.. sexual orientation or like in what context?
yes sexual orientation that is a pattern of romantic attraction to another
Oh okay. It happens naturally over time? Would it be because of biological factors or a result of the environment?
yes its broken up into categories that are aspects of the more nuanced nature of sexual identiy
What different categories are they? Sorry I don't know a whole lot about this and am very curious!
Some people use labels which not all agree with such as "pansexual" or "polysexual"
Does that mean you can be several different orientations at the same time. 
they are generally subsumed under hetersexuality and homosexuality or bisexuality however some can change and revert back.