At the title screen, enter any of the codes below (the numbers refer to the buttons on the Pop'n Music controller, counting from the leftmost to rightmost button in a zigzag pattern) and you should hear a chime. Then play Arcade mode and you will be able to play whatever song or difficulty the code unlocked. For the hyper/EX unlock code, when you play these difficulties in Arcade mode (you must not quit the song partway, but you do not have to pass it) they will be unlocked in Free mode.