How to remove a sensor from the baseplate?

I have a contact sensor which I screwed to a door. I now want to relocate the sensor. When installing, I screwed in the baseplates for the sensor and the magnet, then "clicked" the sensor and magent on the baseplate. When they click in there are plastic tabs on the backside. How do I get the sensor and magnet off the baseplate now? And . . . I have the same question for the motion sensor, how do you get it off the install bracket if you want to relocate it?