Change the email address associated with an Apple ID by signing into your account, clicking on Edit next to the Primary Email Address link and typing in the new email address. After entering the new address, Apple may send a verification email to that address to confirm your ownership of it.
The primary email address on file with Apple in your Apple ID account receives all email notifications from the company, including verification emails. If you are changing the address, you must first sign out of your Apple ID in each instance of programs such as iMessage, FaceTime, iCloud, Find My iPhone and iTunes on your computer and iOS devices. After signing out, visit the My Apple ID page of Apple.com or tap on the Manage My Apple ID link from the iOS device. Both actions bring you to a page on which you must log into the account using your current Apple ID, which is in most cases the primary email address on file.
After signing in, navigate to the email address tab, and enter the new address. In order for the change to take effect, the new email address must not have an association with any Apple ID. If it does, you must change it on that Apple ID before linking it to your current account. After confirming the change, check the new email address for a verification email. Click on the link in the email, then sign into the Apple ID account using the new email address as the Apple ID.