I read a previous thread about pushing a button in on the side, which allows the doorknob to come loose on one side of the door. I have done that.
The thread also said there should be a slot on the periphery of the faceplate where a screwdriver can be inserted to pop the plates off. There is no such slot on these particular plates.
I could cut it off with my oxyacetylene torch, but I may burn the whole door down :-)