How to Reset Any User's Password on a Mac

Resetting Password on a Mac running OS X 10.7 – 10.10

1. 
   Restart your Mac. When your Mac begins its startup process, hold down the "Command" and "R" keys.
2. 
   Open Terminal.

   1. Click "Utilities" in the menu bar.
   2. Select "Terminal".
3. 
   Type "reset password" into Terminal and hit "Enter". This will result in a reset password tool popping up.
4. 
   Select your computer's hard drive. In some isolated cases your computer's hard drive may not show up. This occurs if your hard drive is encrypted and can't be modified with this password tool.
5. 
   Choose a user to reset.
6. 
   Enter a new password. This will become your user's master password, so be sure to remember your change.
7. 
   Click Save. After clicking save, nothing major will happen. The password fields in the form will go blank. Just go ahead and proceed to the next step.
8. 
   Restart your Mac. When your Mac boots, you should be able to log in to the user you forgot the password for.