Play a game and get a game over. On the continue screen, select "No" to go back to the title screen. Now, at the title screen, press and hold Run to go to the main menu. While still holding Run, press Up 3 times, Right 3 times, Down 3 times, Left 3 times. If done right, a sound will be heard. Now start a new game and when you press Run during the game, you'll have the option of restarting the stage.