You can rent a power washer ,and maybe buy mold remover for spray
Here is tutorial I found about this.
Bleach and powerwasher
Use a pump up sprayer to wet the siding down with the diluted bleach/cleaning solution, working from bottom to top. Allow the bleach solution to remain on the siding for 10 minutes or so. Scrub the siding from bottom to top with a long handled, soft bristle brush.
Try Clorox cleanup
On an overcast day when no rain is predicted forvthe next 5 hours, spray well, using a garden sprayer and Wet n' Forget Outdoors liquid (available at Home Stores, Costco, etc.). It will take some months, but will get rid of mold.
If your yard is excessively wet, you'll need to create better drainage, away from house. Install downspout extensions if needed to carry water 10' from your home. Check gutters to make sure they're clear.
Installing copper or zinc at the peak of your roof should resolve algae build up, as well.
Remember if using bleach the plants around the run off area will be affected and possibly die. I use a product from Wal-Mart called crud cutter , apply with a sprayer, either tank sprayer or I use the one that attaches to the house. Let sit for required time. I have what we call a fireman nozzle, usually brass and the tip turns to narrow stream that is like a power washer. Always wash from top to bottom, no sun on part you r doing. Don't wash up so water goes under the siding, always top to bottom.
A BIG THANK YOU to all the answers.