In Monster, if you keep going, every play-through will be different.
You can redesign any room with the Paint Roller icon if you want, but if you really want to clear images, the easiest way is to delete the app and reinstall, this will wipe all saved images.
If you have many players (such as in a school setting), we know this is not the most ideal situation, and we're working on adding in a manual reset that should come in a future version.
