How can I reset my user account password on OS X?
A plausible way of resetting the password of your login on your OS X is to:


Go to Single-user mode (CMD  + S on boot)
Type: /sbin/mount -uw / and press Enter
Type rm /var/db/.applesetupdone and press Enter
Type reboot and press Enter.


On boot, you will be prompted to setup like if your mac was new. Don't panic, as your data is not lost (I would backup just in case though). Skip all unnecessary options, and later you will be prompted to create a new admin account.

Once your setup finishes, from the new account, go to System Preferences > Users and Groups, click on your previous username and click Reset Password. Now type in the new password and login as your old account.