Don't reset it. If you have admin access to the computer's OS X install, just change the startup volume to an external USB with the full OS X installer on it. Mavericks is free from the App Store and you just need to download the installer, mount it or show package contents, copy the
.dmg file to desktop, burn it to a USB stick in Disk Utility. It's a simple process. Then start disk.app and change to the USB, then reinstall OS X.
After you reinstall, open Terminal and write a shell command to use the Unix setregproptool (it's inside the firmware password utility.app contents located in the installer image and also on the recovery partition) and remove the password by calling the remove password command. The program will ask for the previous password over and over until you get it right, without any delay. So, you can easily brute force it. Most likely its a 4-digit pin, 6-digit pin, or 4-8 character password. If it was locked from iOS, (app or online) it's 4-digits. If it was locked from a computer or non-Apple mobile device, it's a 6-digit pin, and if it was locked manually, it is a password. I believe it's 12 characters max, but don't quote me on it. Should only take a couple of days at most.