Rodrigo Da Costa

Esse tutorial serviu pra mim.
 
Shut down your Mac Power up your Mac and immediately press and hold the command + S keys Keep the keys down until you see text on the screen Now enter the following command:
/sbin/fsck -fy
and press enter
Next enter the following command:
/sbin/mount -uw /
and press enter
Now enter the following command:
rm /var/db/.AppleSetupDone
and press enter
Finally, enter the reboot command
and press enter
Your Mac should reboot and you can log in normally, after which point the Setup Assistant will launch. Now you need to create a new admin user. Don't worry, your other user accounts should be intact. NOTE: You should choose a new user name for this admin account.
Once you're back up and running you can go to Apple > System Preferences > Users & Groups and select the Allow user to administer this computer checkbox for the 'grant' user.