Reset Admin password/ unauthorized password change
Resetting User Account Password (10.7 +)


Boot into your Recovery Partition holding down Command + R at the startup chime
Select "Terminal" from your "Utilities" Menu Bar
Type the following command in: resetpassword
From the window that appears, select your boot volume and the appropriate user account
Type in the new password and confirm the new password
Click "Save", close this pane and quit Utilities
Select boot volume again when presented with "Choose Startup Disk" and reboot your machine