iCloud email

To change the iCloud ID ("email") on your iOS device you have to go to Settings>iCloud, tap Delete Account, provide the password for the old ID when prompted to turn off Find My iDevice, then sign back in with the ID you wish to use. If you don't know the password for your old ID, or if it isn't accepted, and if your old ID is an earlier version of your current ID, go to https://appleid.apple.com, click Manage my Apple ID and sign in with your current iCloud ID. Click edit next to the primary email account, change it back to your old email address and save the change. Then edit the name of the account to change it back to your old email address. You can now use your current password to turn off Find My iDevice on your device, even though it prompts you for the password for your old account ID. Then save any photo stream photos that you wish to keep to your camera roll. When finished go to Settings>iCloud, tap Delete Account and choose Delete from My iDevice when prompted (your iCloud data will still be in iCloud). Next, go back to https://appleid.apple.com and change your primary email address and iCloud ID name back to the way it was. Now you can go to Settings>iCloud and sign in with your current iCloud ID and password.

To change the ID on your Mac, sign out, then sign back in with the changed ID. If you only changed your ID and didn't create an entirely new ID, you can choose Delete at all of the prompts when you sign out. This only deletes the data from your Mac, not from iCloud. Your data will download back to your Mac when you sign back in.