If you complete the game and your last save was in levels 15 or 16, you will be able to use cheat codes when starting new game. Don't clear the battery data or save to be able to use this cheat any time you want. Just start new game by pressing Start at title screen, while the starting cutscene is running, press Up, Down, Down, Down, Down, Down, Down, Up, Left, Left, Left, Left, Right, Right, Right, Down, Up then press Start to select any map for 1 player game.