Heavy cloth or canvas awnings take a beating from the sunshine they’re designed to screen out, so regular care and cleaning are essential to preventing (additional) fading and damage. It’s best to read the manufacturer’s recommendations before proceeding.
Wet down the awning and then clean with a solution of mild detergent, such as a dishwashing liquid, using a soft-bristle brush on a pole. Strong cleaners and bleach can damage colors or protective coatings, so proceed cautiously when treating spots or stains. Always pre-test any cleaner in an inconspicuous location. Rinse the awning completely to remove all the dirty solution.
Even if you purchase an extension pole for the brush, you may have to use a stepladder to perform this task. Be careful to keep your balance, and watch your footing since the ladder rungs may get wet. Don’t lean an extension ladder against the awning frame; it isn’t designed to support such a load.
Reference:
Jeff Bredenberg, editor, in Clean It Fast, Clean It Right: The Ultimate Guide to Making Everything You Own Sparkle & Shine.