Can I Delete My save game for something like PlunderNauts?
The easiest way to reset an app if it does not support removal of user content is to remove and then re-install the app.

Any purchase through the App Store can be re-downloaded for free.

In case the download is huge and you do not want to re-download it from the Internet, or in the event that the app is no longer offered on the App Store, you can also transfer the purchases to the computer you use to sync the iPad with and then delete the app from the iPad.  Use iTunes thereafter to re-install it.