How to Reset a Mac’s Administrator Account Password
Use an Existing Administrator Account to Reset Another Administrator Account
Resetting an administrator account isn’t difficult, as long as you have a second administrator account to use. It’s a good idea to have a second administrator account set up for troubleshooting various issues, including forgetting a password.
Of course, that only works if you haven’t also forgotten the password for the other administrator account. If you don’t remember that password either, try one of the other methods outlined below.