how do i reset my mac mini password

What version of OS X are you running? Do you have an Apple ID linked to the user account on your Mac Mini?

If you can answer these questions I can help you! 🙂

Assuming you know your current logon password…

1. Open System Preferences > Users & Groups
2. Click on the padlock icon at the bottom left of the window
3. Enter your current password
4. Click on "Change Password" — at that point you will have two options
   1. Use iCloud Password (the same password you used to log onto this Discussion or…
   2. Change Password
5. In either case you will have to enter your existing password again and then either your iCloud password or your desired new password.

If you have forgotten your current password, you will need to contact Apple Support or better yet get an appointment with the Genius Desk at your nearest Apple Store and take your Mac mini in and have them change it.

OS X: Changing or resetting an account password

or if Lion or later:

OS X Lion>: How to Easily Reset the Administrator Password