This tutorial describes how to reset a user password in OS X.
After completing this tutorial you will be able to reset a user password in OS X without using the original installation disk that came with your Mac. These instructions will only work if a Master Password has been setup previously. For instructions on setting a Master Password, please see http://support.apple.com/kb/PH7032.
From the list of accounts on the login screen, choose the user account.
Choose the "Reset Password" option under the password prompt.
Type the master password.
You will then be prompted to choose a new user password.