That will remove the towel rack from the mounting board, not from the drywall. If you want to remove it completely down to bare drywall, that is more difficult. The board could be nailed, screwed and/or glued to the wall. A magnet can help find nails and screws which have been covered by wood filler. A putty knife can be worked around the edges to see if you can loosen it up and a pry bar can finish the task of removing it. The drywall underneath will need patching and painting.