Apple now refers to an Apple ID as an Apple Account. Changing the account used for iCloud is different from simply changing the email address associated with your existing account.
Steps
- Open Settings and tap your name at the top.
- Review which Apple Account is currently signed in.
- To use a different account for iCloud, sign out and follow the prompts carefully, choosing whether to keep copies of supported data on the iPhone.
- Sign in with the Apple Account you want to use.
Before switching accounts, make sure you understand what happens to iCloud Photos, contacts, messages, backups, purchases, and other synced information. If your goal is only to change your sign-in email or password, edit the existing Apple Account instead of replacing it.