Q: change my iPad password email address from .me to gmail.com to use iTunes match account

Just purchased iTunes Match, works great on phone, trying to upload on iPad.

Apple ID password pops up with old email adddress of @me.com asking for password

iTunes Match will work with my email address of @gmail.com

QUESTION: How can I change the entire AppleID password log in window to display the current email address on my iPad

Got it thanks