How do you change heater core on 1989 Oldsmobile ninety eight regency?

To change the heater core on a 1989 Oldsmobile Ninety-Eight Regency, first disconnect the battery and drain the coolant from the radiator. Remove the dashboard and the HVAC assembly to access the heater core, which is typically located within the firewall. Disconnect the heater hoses from the core, remove any mounting screws, and replace the old core with a new one. Reassemble the components, reconnect the hoses, refill the coolant, and test the heating system for proper operation.