Move all your patio furniture and plants aside.
Sweep debris and remove any weeds.
Hose off any surface dirt.
Choose a chemical cleaning agent such as Borax,vinegar, or oxygen bleach to remove tough mildew stains.
Power wash or scrub by hand with a stiff wire brush.
Spray a salt and vinegar solution in the cracks to prevent further weed growth.
Lay down compacted polymeric sand to create a physical barrier to weed growth in the cracks.
Seal your cleaned bricks with a low glosswater-based sealant