- Start System Preferences and select "Accounts".
- Under the list of users press the "Login Options", and then next to that press the "Join..." button next to Network Account Server. (You will not be joining a network account server, this is just the convoluted way to get to the Directory Utility).
- Press the button to "Open Directory Utility..."
- Click on the Lock icon and give the Administrator password to authenticate.
- Pull down the "Edit" menu to "Enable Root User"
- Pull down the "Edit" menu to "Change Root Password..." and enter a good, strong password for the root user.