A screwless deadbolt is not attached to the door with screws on the outside of the deadbolt. Instead, the screws are under the plate of the lock. This can make the deadbolt difficult to remove if you want to replace the lock, but if you remove the plate you should be able to access the screws behind it.
Slide the deadbolt in place with the key, if needed.
Pry up the plate from the door, using a flathead screwdriver, if necessary.
Remove all of the screws behind the plate and remove the lock's cover.
Unscrew the screws around the thumb turn and the bolt mechanism of the deadbolt.
Slide the deadbolt out of the lock and remove the pieces of the screwless deadbolt from the door.