my icloud is attached to an apple ID that is not my primary and I can't get it to change

I have recently downloaded OS8.

I did it using my macbook pro via itunes and then synced my phone.

since then i keep getting a message to sign into my iCloud on my phone

sounds great except is is showing an incorrect apple id email and won't accept my password.

I have tried changing the password but that is not the issue - the issue is the wrong email address and I can't change this over

can anyone help?

thanks

Sharon