How do you change heater core in 2005 Chevy Express?

To change the heater core in a 2005 Chevy Express, start by disconnecting the battery and draining the coolant. Remove the dashboard and the HVAC unit to access the heater core, which is typically located behind the dashboard on the passenger side. Disconnect the heater core hoses and any mounting screws, then replace the old core with the new one. Reassemble the HVAC unit and dashboard, refill the coolant, and reconnect the battery.