How to Modify MacBook User Accounts
Consider the basic modifications that you can make to a MacBook user account, such as changing existing information or selecting a new picture to represent that user's unique personality. To edit an existing account, log in with your admin account, display the System Preferences window, and click Users & Groups to display the account list. Then follow these steps:
In the list to the left of the window, click the account that you want to change.
If the accounts in the list are disabled and you can't select one, you must unlock the Users & Groups pane. Click the lock at the bottom left of the System Preferences pane (and type your password, if prompted).
Edit the settings that you need to change.
Examples include enabling administrator rights for an account temporarily (by selecting the Allow User to Administer This Computer check box) and changing the account password (by clicking the Change Password button).
Click the square picture well (the square that displays the image) to specify the thumbnail image that appears in the Login list next to the account name.
Apple provides a number of good images in the preview collection. Just click a thumbnail to select it.
To replace your account image, drag a new image from a Finder window or the iPhoto window and drop it into the picture well.
To choose an image from the default set of Mountain Lion icons: Click the picture well, click the Defaults tab, click the desired image, and then click Done.
To choose an icon image from those you've recently used: Click the Recents tab, click the desired image, and then click Done.
Alternatively, you can click the picture well and click the Camera tab to grab a picture from your MacBook's built-in FaceTime HD camera. When you're set to take the photo, click the camera icon and then click Done to accept it. Most cool.
After you make your changes, press cmd+Q to save them and close the System Preferences window.
Standard-level users have some control over their accounts. Standard users can log in, open System Preferences, and click Users & Groups to change the account password or picture as well as the my Card assigned to them in the Mountain Lion Contacts application. All standard users can also set up login items. Note, however, that managed users might not have access to System Preferences, so they can't make changes.