Why yes there is.
It is different than the older games, rather than just starting a New Game and overwriting your old game, you must first input a certain button combination to delete your old data before creating new data.
The combination to reset your data and delete it is in the title screen, than follow the following commands:
" Up, SELECT, and B simultaneously".
You will also want to reset your Pokewalker to make it compatible with your new game.
To do so, first go to "Connect to Pokewalker" in the Main Menu.*
From there, follow the steps:
- Hold DOWN and X, than press L.
*If you have deleted your Saved game and did not reset your Pokewalker, go to "Connect to Pokewalker".
From there, press "Go for a Stroll" first, than enter the above commands.
Taken directly from the booklet. Good luck! ~