How do you replace a heater core on a cutlass 1981?

To replace the heater core on a 1981 Cutlass, start by disconnecting the battery and draining the coolant from the radiator. Remove the dashboard and the heater box by disconnecting the necessary wiring and fasteners. Once the heater box is accessible, take out the old heater core and install the new one, ensuring proper sealing. Finally, reassemble the dashboard, reconnect the battery, and refill the cooling system with coolant.