Luckily, it's pretty easy, and there are several ways to change the administrator name in Windows 11. As long as you already have access to the administrator account, you can change the name to ...

If you are unable to change the domain name in Windows 11/10/Server, fix the Name resolution (DNS) issues and update the Group Policy settings.

To change the name of a user profile folder in Windows 11, sign out of that user account and sign in with another user account. Also, make sure that you are signed in as an administrator.

These are the common settings I personally change on every Windows 11 installation.