Not a fun job. Here are the directions I found for you.
1. Disconnect the battery.
2. Drain and recycle the engine coolant.
3. Remove the instrument panel. Refer to.
4. Compress the holding tabs and disconnect the heater water hoses at the heater core.
5. Remove the A/C plenum demister screw and remove the A/C plenum demister adapter.
6. Disconnect the vacuum line.
7. Remove the heater core bracket.
8. Remove the 13 retaining screws and remove the plenum chamber top.
9. Remove the blend door assembly from the case.
10. Remove the heater core. To install: 11. The installation is the reverse of the removal.