go to 'delete games' screen. (I usually go there by clicking on a game that is under 3 moves old). the screen has a tick box text to all the games that are under 3 moves old and games that are past TO. Check the box of the game you wish to delete (if necessary uncheck the box of any games you wish to keep), update, and the game disappears without rating changes.
At least this used to work, but it may have been removed. Let me know how you get on.