If you should use Home Edition the procedure is a little bit different. In 'control userpasswords2' on the user tab first check 'Users must insert username and password'. Then the list of users below it will no longer be grayed out. Click on 'Guest', then on properties and change the name. Click OK. Back on the main window click 'apply', then untick the 'Users must insert...' box again. Click OK. In the window that pops up then also click OK, and done.