Replacing a heater core in an Audi A6?

I have a 1996 Audi A6 Quattro, I bought it used, it's in very good shape except the heater core went out of it. I bought another one on ebay, but spent 3 days trying to figure out how to remove the old one and replace it. I gave up due to exhaustion and frustration. There are no Audi dealerships within 50 miles of me, and it's too cold to drive it very far. I'd hate to imagine the cost, I'm on unemployment right now so every penny counts. Does anybody have an idea about what I need to do to fix it? Thanks a lot!