How do you replace a heater core in a 1990 Oldsmobile Cutlass Supreme SL 3.1L V6?

first look on the back of th engine there should be two heating lines running into the firewall.when you see where they run into the firewall go inside the car and remove all of the pieces under the dash.if you got it right it should look like a very small radiator,remove all necessary mounting screws or bolts.go back into the engine bay and unclamp the two heating lines that run into the firewall and that should be about it.

good luck to whomever