How to Change Users in Mountain Lion
Circumstances might dictate that you need to change a user’s identity, password, or accessibility, or perhaps delete a user from your Mac running OS X Mountain Lion. Follow these steps to change a user’s name, password, or account type:
Choose Apple→System Preferences (or click the System Preferences icon in the Dock or Launchpad).
The System Preferences window appears.
In the System Preferences window, click the Users & Groups icon.
The Users & Groups System Preferences pane appears.
If the lock icon at the bottom of the window is locked, you have to click it and provide an administrator password before you can proceed.
Select the user’s name in the accounts list.
The information for that person appears.
Make your changes by selecting the existing username and replacing the old with new text or a different setting.
If you want to change the password, click the Reset Password button and make your changes in the sheet that appears.
To change the picture or other capabilities, click the Picture, Login Options, Allow User to Administer This Computer (to enable or disable administrator privileges), or Enable Parental Control check box (more on this in a moment) and make the appropriate changes.
To change a user, you must be logged in using an account that has administrator powers.
Quit the System Preferences application or choose a different System Preferences pane.
Your changes are saved when you leave the Users & Groups pane.