how do you clean cement patio?
Spray bleach on it let it set a few min spray it off with water.
You can use a power washer with a cleaner in the tank or you can use a good stiff garage broom, buckets of warm water with a cleaning solution, give it a good scrub and rinse with your garden hose. Take everything off the patio, clean it well, and let it dry all the way before you replace anything. If you do not own a power washer you may be able to rent one in your area.
I pressure wash and if it's particularly bad, use Krud Kutter. Wet & Forget Outdoor is great for preventing build up.
Here's a great post on cleaning cement easily.
Scrub it with a power washer. If you can't buy one, rent or borrow! Then seal the driveway with a good concrete sealer. The stuff is pricey, but worth the investment. It cleans easily after that. Now, we clean ours at least once per year, just hosing it off in between. Reseal every 3-4 years.