iCloud email on iPad

If you need to change the email address that identifies your AppleID account - as used to sign-in to iCloud and other Apple services - the procedure is quite simple:

Change your Apple ID - Apple Support

What to do after you change your Apple ID or password - Apple Support

If you are attempting to do something else, you’ll need to provide some additional explanation.

If you are updating your AppleID account, you only need to perform the change for account (the first link) from one of your devices. Having made the update, you’ll need to perform necessary follow-up changes (the second link) for each of your devices.

the email is tied to your appleID if you change your appleId it will be as if you are starting out from new in terms of downloads and purchases