How to Change an Apple ID & iCloud Account in Mac OS X
All users should have their own Apple ID, which is tied not only to an iCloud account, Messages, FaceTime, App Store, iTunes, iBooks, and Passbook with ApplePay, but in new versions of Mac OS X an Apple ID can also be used to log into a Mac user account too. Because each Mac user should have their own unique Apple ID for their own devices, it can sometimes be necessary to change an Apple ID associated with an iOS device or, in this case, a Mac running MacOS X.