Unscrew the cover over the heater core to expose the core. Assuming you've already disconnected the heater hoses, you can now gently jockey the heater core out, complete with the heater control valve attached. Here's the core with the old heater valve attached. After removing the old valve, I cleaned up the core's mating surface with scotchbrite. Here's the core with the new heater valve attached.
Installation is the reverse of removal.
Be sure to top off and bleed the engine coolant. See the TSN Parts FAQ for vendors. The content on this site may not be republished without permission.