changing the administrator name

Make sure to have good verified working backups before doing anything else since so many people end up making a mistake when trying to make this change. Here is an Apple article on how to change the user account name:

https://support.apple.com/en-us/HT201548

Make sure to follow the instructions carefully or you will temporarily lose access to your account and data.

DON'T do that!

Users who attempt to change Account names OFTEN end up locked out of their Mac.

Instead, Create a NEW Admin user with the name you prefer, and login as the new user. then you can copy files around, and get the new user set up to your liking.

If, after a week on the new Admin user, you find you have not referenced anything on the old user, you can delete the old user and its files.