Eu achei encontrando essa solução e várias pessoas disseram que deu certo. vou tentar ela pra ver se resolve meu problema. Vou fazer agora o que você me disse pra ver se consigo.
Solução:
Even though the Setup Assistant only runs once when you first install Mac OS X / macOS, it remains on your computer and is prevented from running by the presences of a hidden file called ‘.AppleSetupDone‘ in a system folder on your Mac. Therefore, to have the Setup Assistant run again so you can create a fresh admin account, you simply need to remove this file:
1 - Reboot your Mac and hold ‘Command-S‘ at the boot chimes to load into Single User mode.
2 - At the command prompt, run the following command to make the filesystem writable: mount -uw /
3 - Run the following command to remove the hidden file: rm /var/db/.AppleSetupDone
4 - When complete, enter ‘reboot‘ and the prompt to restart the system, and you will now see the Setup Assistant load when OS X starts up.
5 - Proceed through its various screens, and create your new account. You might consider using a different username than any previous accounts on the system, to ensure there are no conflicts with the present and faulty accounts.
6 - Now you can log into the new admin account, and better manage the prior ones on your system, including deleting and recreating them accordingly.