It’s very easy, just spray down with your water hose. You can also use a mild soap/water mix if your garage screen is extra dirty and dusty. Put some water in a bucket (or whatever you have) and add a few drops of dish soap. You want just enough soap to make some bubbles, then simply use a sponge to wipe down your screen and rinse as you go along. Do not use harsh chemicals or soaps like bleach or strong concentrated soaps.