Remove the ceiling vent by backing out the screws that hold it to the ceiling. If the ceiling vent has been painted into place, cut the paint at the edge of the vent using a sharp utility knife.
Remove ventilation pipes from the attic by pulling them up out of the ceiling. Cover the hole in the ceiling from underneath before you do this or you will have ventilation falling into the room below. Disconnect the ventilation pipe from the attic ceiling where it exits the house and remove it from the attic.
Remove the vent stack from the roof by cutting through the roofing tar around its base and prying it off the roof. Fix the hole that remains where the vent stack was by fitting matching asphalt shingles into the space.