OS X: Changing or resetting an account password: "Start up from a Mac OS X Install disc (one whose version is closest to the version of Mac OS X installed). Usually, you can start from the disc by putting it in your computer, restarting, and holding the C key. Or, put it in the computer and click the Install or Restore icon you see in the disc's main window (after which the computer will start from the disc without you needing to hold C). Or, you can use Startup Manager or the Startup Disk preference pane to select the Install disc.
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