Question: Unable to unlock system preference
i tried to change the account name because i wanted to change the user name (it was mac and i wanted it to have my name). Doing so, the admin user has now changed to standard. Also, i am not being able to unlock the lock to make changes in the system preference even if i enter the correct admin name(mac) and the correct password for it. please help me with it.
MacBook Pro (Retina, 15-inch, Early 2013), macOS High Sierra (10.13.2)