How to Remove Users from Your Mac Running Mountain Lion
To delete a user from your Mac running OS X Mountain Lion — in effect, to deny that user access to your Mac through file sharing — select the user you want to delete in the list of accounts and click the – button. A sheet appears, offering three choices:
Save the Home folder in a disk image saves a disk image of the user’s Home folder in a folder named Deleted Users (which it creates inside the Users folder).
Don’t change the Home folder removes the user from the Users & Groups System Preferences pane and login screen but leaves that user’s Home folder in the Users folder. (Deleted) is appended to the folder’s name, so if you selected this option, Steve Wozniak’s Home folder would be renamed steve (Deleted).
Delete the Home folder does what it says. You have the option of a secure erase (the contents get overwritten multiple times) if you select this option.
To remove a user from your Mac, you must be logged in using an account that has administrator permissions. And you can’t remove the first user ever created on this Mac.