Instructions
Put the "Pokemon SoulSilver" cartridge in your Nintendo DS and boot it up.
Go to the title screen of "Pokemon SoulSilver," hold down the "B" and "Select" buttons and press the "Up" button on the D-pad.
Select "Yes" when the prompt comes up asking if you want to delete all of your game data.
Select "Yes" again when the second prompt comes up warning you that this will erase all of your data forever.
Proceed to the game's main menu and select "New Game."