Demolishing a wood deck is always easier than building one. The demolition tools used to tear a deck down can be found at most hardware or home improvement stores. The tools aren't too expensive and are multi-purpose tools which can be used again and again making the investment worthwhile. A deck is built from the bottom to top and is torn down from top to bottom. Nailed on decking is easier to remove than screwed on deck boards, but the right leveraging tool takes care of both.
Put on a pair of work gloves and safety glasses.
Swing a sledgehammer into the handrails to topple them off the deck. Strike all spindles to break them off.
Stick the flat edge of a pickax under the spindle baseboard and pry it up out of the underlying deck boards. You may have to stick and pry in several places. Swing and stick it under the board wherever a nail or screw holds it down. Pull on the handle of the pickax to pry it up.
Pry up the outmost deck boards from the underlying floor joists with the pick axe the same way the spindle baseboard was pried up. Pry up and remove one deck board at a time until all deck boards have been lifted and removed. Work from the outside of the deck inward.
Strike the ends of the floor joists where they are fastened to the hangers with the sledgehammer to bust them loose. If the sledgehammer isn't doing the job then cut the joists off with a reciprocating saw at both ends.
Pry the hanger boards away from the foundation with the pickax if the deck was attached to a foundation. Bust all the outer hanger boards off the deck support posts with the sledgehammer. Remove the hanger boards from the area.
Dig around the concrete footings with a shovel and pull back and forth on the deck support posts until they can be pulled out of the ground. Load the footings into a wheelbarrow and haul them off.
Bust up the deck steps with the sledgehammer and haul them off. Dig around the cement footings that supported the steps until they are loose and then lift them into the wheelbarrow and haul them off.