If you're done with the printing the image in the screen, use emulsion remover to get the emulsion off and reset your screen. Emulsion remover is available at your local art supplier and it's in a bottle that looks a lot like the emulsion container. This particular emulsion remover came in a kit along with the emulsion.
Put it in a spray bottle and mist your screen with it, letting it soak in. The emulsion will come right off with a little elbow grease.