- Hold during boot cmd+R
- Click on the top left scheen on the 'Utilities' menu and then on 'Terminal'
- When Terminal is open typ 'resetpassword' and press enter
- Hold during boot cmd+S
- Type 'mount -uw /' and press enter
- Type 'launchctl load /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist' and hit enter
- After this you can reset any username with 'passwd username'