Tear the carpet up from the stairs, exposing the particle board treads.
Start at the topmost stair. Pry up any nails holding the stair tread to the stringers and the riser, using a pry bar and a hammer.
Unscrew any screws that hold the tread to the riser using a screwdriver.
Break the adhesive bond between the stair tread and the riser and stringers using the pry bar and hammer. Place the tip of the pry bar under the lip of the tread. Hit the end of the bar with the hammer to drive it between the tread and the riser, lifting it up. Move the pry bar across by about 4 inches and repeat.
Pry the tread up all the way around until you can lift it up without any trouble. Repeat with any other steps that you want to remove the particle board stair tread.