My mom has a score set on my iPod touch and I can't beat it , is there a way I can reset the score to zero and start all over?
If the high score is stored locally (= you didn't sign up) deleting and reinstalling the application should do.
For apps purchased via the Apple App store, simply deleting the application by holding the icon until it "wiggles", and then pressing the "X" in the corner of the icon should remove it.
Reinstall the App
Then, navigate back to the App Store, search for Veggie Samurai again, and you can install the app again. You will have to select "Buy" again, but once you do, it will remember and say "You have already purchased this app", and will allow you to download it again for free.
With iOS 5, Apple added a new way to download apps you've already bought! Clicking on updates in the App Store app will bring up the usual list of programs that have updates available. However, at the top you should see this:
Click on the purchased button, and then select "Not on this iPhone", and navigate down to re-install the app.