Question: how to reset administrator username and password on mac?
Answer: Restart your Mac. ... 
While it is restarting, press and hold the Command + R keys until you see the Apple logo. ... 
Go to the Apple Menu at the top and click Utilities. ... 
Then click Terminal.
Type “resetpassword” in the terminal window. ... 
Then hit Enter. ... 
Type your password and a hint. ... 
Finally, click Restart.