You have to drill them out.
Take a drill bit that is a little smaller than the plug and drill them out at a low speed. There will be screws underneath the plugs so be careful not to damage the heads with the drill bit. You can use a small screwdriver to remove the rest of the plugs once there is a hole. You can get new plugs at just about any marine store. I have even seen them at Lowe's. Put some glue on them, tap them into place and cut off the excess. Sand until they are flush. Easy enough?
