Apply a fungicidal wash, available for purchase at many hardware or garden supply stores, to the affected area. Wear gloves and protective eye wear and apply the wash during dry weather when there will be at least a few days of sun.
Wait three to four days after application for the wash to dry up and kill the organisms in the lichen.
Scrub the dried lichen off the concrete with a long-handled stiff cleaning brush.
Spray the area with water to rinse, using a garden hose or power sprayer or by pouring buckets of water over the concrete. Consider adding an anti-vegetation detergent to the water for increased prevention of future growth.
Scrub away lichen with the long-handled brush as soon as it begins to grow on concrete, and then rinse well.