Detach It

• If the plywood is nailed or screwed into the wall studs, one of the simplest ways to remove it is to just pry up the nails or unscrew the screws. A claw hammer will pull the nails out of the wood, and a power screwdriver set to reverse will remove the screws quite easily. You may have to scrape away paint or other wall coverings to expose the fasteners before you can remove them, however.
  
  

Pry It Loose

• If the plywood is held on with glue or you just don't particularly fancy going after the fasteners one-at-a-time, you may be able to use a prybar and pull the entire piece of wood away from the wall using leverage. Be careful if you use this method to make sure your prybar has a stud underneath it to use for levering support; if the prybar is supported just by drywall there's a chance you'll end up with a hole in your wood.
  
  

Cut It Out

• If you just need to repair or replace a smaller piece of plywood, your best option may be to just use a power saw to cut the section out completely. A skilsaw or Sawzall -- two hand-held power saws, the former with a circular blade and the latter with a straight-out blade -- should cut through the plywood with little trouble and enable you to remove the offending section completely. Be careful about cutting into the stud behind the plywood and be very careful you do not guide the saw blade into any nails.
  
  

Bash It In

• By far the simplest -- and often the most satisfying -- method of removing plywood from a wall is to simply destroy both the plywood and the wall at the same time. A few good swings from a sturdy ax or sledgehammer will demolish the plywood and allow you to simply rip it away from the wall with your bare hands. This is not the recommended if you want to keep the wall behind the plywood intact, however.