Instructions
Turn on your Nintendo DS.
Tap the bottom screen to get to the main menu, and then tap the icon for "Nintendogs."
Hold down the button with the letters "A" "B" "Y" "X" and also the "Left" and "Right" buttons on the back of the Nintendo DS, at the same time before the game loads. A screen should appear to confirm that you want to delete your data. Tap "Yes." Another confirmation screen will appear; click "Yes" again.