OS X 10.7 Lion, 10.8 MountainLion & 10.9 Mavericks
Reset Password using Recovery HD
Boot into Recovery Partition.
Start the computer,then press and hold down command and R keys to start into recovery partition.
When you see the Apple logo, release the keys.
Wait until OS X Utilities window shows up.
Move the mouse to the menubar at the top and click "Utilities", then select "Terminal"
from the drop down.
Terminal window will appear.
Type in resetpassword and press enter on the keyboard.
Leave the Terminal window open.
Reset Password Utility window will open with Macintosh HD selected.
Select the user account from the popup menu box.
Enter a new password.
Reenter the new password for the user.
Enter a hint.
Click the "Save" button.
Click in the menubar and select Restart.
If Keychain dialog box appears, select “Create New Keychain”.
When selecting passwords, make sure it's one that you will NEVER forget AND no one else can figure out.
Old school--- > Print it out & keep in a safe place. A place that ONLY you know about AND never forget.
New school---> Get a password manager utility. Highly recommend 1Password which is shareware. Do a Google search for free password managers.