Q: I just tried to transfer all of my contacts etc to a new iphone. For some reason it put an old apple id on the new phone and I can't fix it

I just got a new iphone 6S. I connected my old iphone 5s to itunes and hit back up now. I then connected my new phone and hit restore to transfer all of my contacts etc. For some reason it put an old apple id on my new phone and I can't figure out how to change it. Whenever I try to do anything, it asks for the password for the old apple id and when I enter it, it just says your id or password are incorrect. Help!