Can anyone tell/explin how to property replace the points on a D model PumpTro control switch ( very old switch about 1980 ) Bill

Never heard of doing that. You can clean them to a certain extent with a few strokes with an emory board. If you're talking about a switch similar to the one in the link below, they are fairly cheap and not difficult to replace.

Amazon.com: Square D Co. FSG2J21BP Pumptrol Pressure Switches: Home Improvement