A lot of people get confused when trying to change the iCloud email login on their iOS devices (iPhone, iPad, iPod Touch, etc.).
There are two reasons for this: one, if you have an @iCloud.com email address linked to your Apple ID, you can’t change it; two, if you want to change the iCloud account and Apple ID that goes on your iOS device, the option is called “Delete Account”, which terrifyingly sounds like everything you have backed up to iCloud will be deleted.
This is not the case ? everything associated with the old iCloud email login will still be available in the cloud, it just won’t be linked to the device you delete it from anymore.
A third option is to add secondary email accounts to your iCloud email login using the Apple ID management page. To do this, login to appleid.apple.com with your iCloud email login information, and then click on “Manage” your Apple ID.
How do unlock Apple ID