To remove a roof vent cap, you need a screwdriver, utility knife, extension ladder, cat's paw pry bar and a hammer. This is fairly easy to do, but you need to be careful since you need to access the roof to remove the roof vent cap.
Access the vent pipe from the attic and follow it to the roof. Look for the pipe clamp, loosen it with the help of a screwdriver and remove it. Make sure that the extension ladder is well anchored before getting on the roof. Bring the hammer, utility knife and cat's paw pry bar with you to the roof in a tool belt.
Peel back the shingles in order to expose the nails that hold the flange onto the roof. If the shingles are covered with tar, remove them with a utility knife. Use the cat's paw pry bar to pull all of the nails up, but do not throw them away. Save the nail in a tool belt, as you need to reinstall the vent cap. Pull the vent cap straight up when all of the nails are removed. If it seems difficult, a slight twist may be needed to fully remove the vent.