Bucket of hot water with detergent and bleach and a soft bristle brush on an adjustable pole.
Wash sections that are in the shade moving around the home as the sun moves. Wet a section first with a garden hose then scrub starting at the bottom and moving up (this will avoid streaking) Don’t the let the solution dry on the siding and be sure to rinse thoroughly.
Make sure you protect nearby plants from the bleach solution by either covering them or rinsing them frequently.
