How Do I Change My Apple ID Email Address?
You cannot change the email for your Apple ID if it's an Apple email (@icloud.com, @me.com, or @mac.com address). You are able to add an additional email though. All others can change their email.
Go to My Apple ID and sign in your with account credentials. Click "Edit" to change the address or click on "Add Email Address" to add another to your account.
If you have changed your email, you will have to log out and log back in on any devices/apps that use iCloud (Mac, iPad, iPhone, iTunes, App Store, etc.).