Here is information about how to reset or change your Root password in Linux Mint.
Hold Shift on boot
Unless you already see the Grub-loader every time you boot your computer, then, on boot, press and hold the Shift-key until you get the Grub-loader menu on your screen.
Your cursor will probably already be standing on the correct line (“Linux Mint, with Linux x.x.x-xx-generic” if you are running Linux Mint) so press E on the keyboard.
Go to the Kernel-line
Go down to the “kernel-line” which is the line that begins with “linux /boot/vmlinuz…”.
Change ro to rw
Locate the “ro” (without quotes) and change it to “rw” (once again without quotes), this changes the file system mount from read only to read/write.
Then go to the end of the line and add:
Depending on your normal character set your = and / characters might be on some other key than you are used to, but keep trying until you find out how to write them. 🙂
Then press F10 on the keyboard to launch with these settings.
Run the passwd command
After a short while you should have a command/shell prompt right in front of you, enter “passwd” (without quotes) and press enter, then write your new password and press enter, and then you’ll have to write it again to confirm it.
After that you can press Ctrl+Alt+Del to reboot