If admin account name is changed and converted into standard account , enter in single user mode .
- Choose Apple menu > Restart, or press the power button if your Mac is turned off.
- Press Command-S as your Mac starts up.
The screen is black with standard white text. You can now run the UNIX commands that you want.
- Execute this command .
mv /var/db/.AppleSetupDone /var/db/.OldAppleSetupDone
Then press enter key after that .
Restart the Mac , then it will prompt language then create a new user account .
Note : in the first terminal command there is space after mv and also after AppleSetupDone