How do you change the heater core in a 1992 Ford Tempo GL with air conditioning?

I have this same kind of car w/ a 3.0 L V-6. And thought my heater core went out but it's actually just leaky. It's located behind the dash, locate the floor vent, and basically..its just above that. It's a job and a half, very time consuming and extremely frustrating. I'd recommend taking it to a trust worthy garage and have them do it. The heater core itself isn't that expensive, but after you have someone install it, you wouldn't believe it.