You start with a sodium hydroxide stripper, a liquid one rather than a paste. Cabots distributes a good system. You can apply this stuff with a compression sprayer or use brushes and rollers. Keep the stripper moist for at least an hour, longer if the stain resists softening, by misting it with water. When the stain softens, scrub the deck with a stiff broom and wash the deck using a power washer. Neuturalize the stripper with white vinegar and rinse well. Allow to dry overnight.
The next step, you have a choice. You can use a "wood brightener" or I just use household bleach, mixed 1 to 1 with water. Saturate the wood and keep it saturated for a couple of hours, then rinse it well using the power washer to flood it with water.
When the deck is thoroughly dry (expect to let it dry for several days) Seal it or stain it as per material drections.