You will need to rent a hot water pressure washer. Prep area to be cleaned with a broom or blower to remove all debris. Any ground plants lying on area need to be held back or protected due to hot water. There is an array of concrete cleaners on the market, but some suitable cleaners can be purchased at your local Auto Zone. Be sure to wear protective gear goggles, long pants, and log sleeves gloves, while applying and while pressure washing area with solution. Also follow mixing instructions on container to your needs. You will need a coarse yet dense brush to rub in cleaner, possibly a wire brush for tougher stains. allow to set in at least 15 minutes with hot high pressure water start cleaning in an area with least amount of cleaner, try to stay with a consistent back and forth movement of the wand roughly 3″ from surface. Be careful of corner areas for you may experience splash back. If your working on a sand based brick walk or patio, be sure to have a variable pressure wand and use the least amount of pressure to get the job done.