Ron's correct in that these tiles are nailed up, using a round headed copper (in your case) nail. You will have to determine in which direction they ran the tile in order to remove it. Using a "nibbing" pliers, sort of like tile cutters, will allow you to get under the nail heads. Maybe placing a thing piece (1/4") of wood on a tile to pry on will prevent damaging an adjoining tile. Personally--I'd try to remove these and save them. Modern ceiling materials just cannot match these for beauty. Good Luck and post photos of the finished project.