In Ubuntu, if you can believe this, it’s quite easy to change or “reset” the password for an account, so long as you have physical access to the machine. In total this should take you about 10 seconds to finish, give or take for the actual speed of the machine. More here
First restart, and then watch closely as the computer starts up again. After the BIOS screen disappears (the screen that usually shows the manufacturer’s logo, or information about the hardware), hold down the Shift key (if you’re using a version earlier than Karmic, you will probably have to press Esc repeatedly).