How to reset your apple id if the email associated with the account is no longer in use?
How to reset your apple id on your iPad mini if the email associated with the account is no longer in use?
Note the restrictions in the article.
Make sure you turn off Find My Phone before signing out of the old ID. Once signed out and Find My Phone is off, then sign in with the new ID, then turn Find My Phone back on.
What to do after you change your Apple ID or password - Apple Support * I suggest doing this before you change your Apple ID or password.