When you buy a used copy of DragonBall Z: Supersonic Warriors 2 for the Nintendo DS, you may find the game starts at a previously saved location. If you want to start the game from the beginning, corrupting the save file is your only option. It may take several tries to complete the task, but when you do you will have a completely clean cartridge, which will allow you to play the game from the beginning.
Turn on the game.
Select the options menu.
Pick a random option and change it.
Put your cursor over the exit option, but do not press A yet.
Press down on the cartridge. Do not release it from the slot.
Hit "A" and release the cartridge at the same time.
The screen should state "data corrupt" or otherwise indicate it cannot read your cartridge.
Turn off the system.
Insert the cartridge into the game slot.
Re-start the game. The game should now start from the beginning.