How do I find my administrator username on my Mac ?

Find user name

If you cannot login:

How to find the username using Recovery HD without resetting password?

We are not going to reset password here but just find the username.

macOS Sierra 10.12 and macOS High Sierra 10.13

Shutdown the computer.

Start the computer, then press and hold down command and R keys to start from macOS Recovery.

When you see the Apple logo and the progress bar, release the keys.

You have to press hard the Trackpad to register the click.

Select the “Language”, if not already.

Click the arrow button at the bottom.

Wait until OS X Utilities window shows up.

Move the mouse pointer to the menubar at the very top of the screen, click "Utilities” and then select "Terminal"

from the dropdown.

Terminal window will appear.

Type in resetpassword and press enter on the keyboard.

Reset Password window will open revealing all user names.

Quit from . Select Startup Disk.

Simply opening your terminal.app found in your Application/Utilities folder and copy and paste:

dscacheutil -q group -a name admin

this will return admin(s) name on your computer.

copy and paste:

dscl . list /Users | grep -v '_'

will return all user names

I tried to change my username but suddenly my account has been changed to "standard" and now every time I want to unlock to make changes, it asks for the administrator username and password and it does not accept my username and password.

I did that, but the problem still exist.