Forgetting your password means that the only way to recover it or change it is to use MAC installation CD or follow these steps:
"System preferences" using the Apple logo
- Click the
"Lock icon" on the lower left side of the
"Accounts" section and enter the newly created user credentials which enables you to change other user accounts and reset other users passwords.
- On the left side chose the username you wish to change the password for
- Click on the
"Reset Password" button
- Enter a new password for the user selected
"System preferences" and reboot your MAC
- Boot up and use your new password.