There might be an easier way, but you could try this.
You could start by removing the game and the user data and then re-installing the game. From what I've read, that probably won't be enough, but you could try that first.
There should be a robo_defense_full.bak file in the root directory of your internal storage. I've read that the game will use that file, if it exists, to restore your game data after a re-install. So, you may have to remove the game and that file, and then re-install. You might want to keep that .bak file and just rename or move it, so the game can't find it. Then if you decide that you want to put things back the way they were, you might be able to do that by just putting that .bak file back in place.
You could also try getting rid of the robo_defense_full.bak file without removing the game. My guess is that that file is just a backup of the game data and you need to remove the game too, but you could try removing just the file and see what happens.
Hope this helps.