In order to remove the heater core, the AC system has to be discharged of the refrigerent. The steering column has to be removed, then the entire instrument panel(dashboard) assembly, and finally the HVAC housing has to come out in order to remove the heater core. This is about an 8hr job at a shop.
If you still want directions, let me know and I will provide them, but it will take about 20 minutes to upload all the directions
here you go:
Click to open and download> STEERING COLUMN