How can I change my apple id associated with icloud. I have signed into my apple id on windows and can't see where to change it

I have updated to iphone 6. The icloud id is an old email address I have not had access to for years. I cannot see in my apple id where I can change it to match my itunes apple id. I want everything to match. It keeps coming up on the phone to enter the password and I can't remember or it re-set it

when i tried to reset it it reset my itunes apple id.