changing the administrator name

Hi thatguy-,

Grant Bennet-Alder has the safest advice here; just make a new administrator account.

In fact, if you want to start clean with the Mac (which I'd recommend if you don't need any of the current data on it), erase it and then reinstall macOS:

How to erase an Intel-based Mac - Apple Support

How to erase a Mac with Apple silicon - Apple Support

How to reinstall macOS - Apple Support

If you absolutely need to retain the old account but want to rename it, follow the below steps from Apple. Before completing them, create a new administrator account, log out of your current account, and then log in to the new administrator account.

FAILURE TO DO THIS COULD CAUSE DATA CORRUPTION.

Change the name of your macOS user account and home folder - Apple Support

DON'T do that!

Users who try to change the username often end up locked out of their computer and their files are lost.

Instead, create a NEW Admin user (there is no maximum number of Admin users) and log in with the new Admin Account. If you don't need any of the old stuff after a week or more, you can delete the old account.