Why should I change?
Because you want to.
We are not here to tell anyone that they need to change. That sort of directive only leads to judgment and bigotry despite all good intentions.
So, if you don't want to change, don't. You couldn't if you tried. But if you do want to change your sexuality, you can. It is possible. But only if you truly want to and are willing to follow God into scary territory.
All we ask is respect for that truth. Sexuality is a crazy complex thing, and it is that very complexity that allows someone to change their sexual orientation. No one is only one thing. Only you can decide which part of your sexuality you feel most comfortable with. You may not feel any heterosexual part in yourself, but it is there, and if you desire to embrace it, you can.