How do you replace the heater core on a 2003 Pontiac Grand pirx?

To replace the heater core on a 2003 Pontiac Grand Prix, first, disconnect the battery and drain the coolant. Remove the dashboard, which involves taking out the center console, trim pieces, and bolts securing the dash. Then, access the heater core by removing the HVAC housing and disconnecting the heater core hoses. Replace the old heater core with a new one, reassemble the HVAC housing, and re-install the dashboard before refilling the coolant and reconnecting the battery.