How to remove the heater core on 1999 Mercury Grand Marquis

What needs done to remove the heater core from my car. It needs replacement and need to expert way to get at it.

This is a really involved job, including removing the seats, carpet, steering column and much more.
I can't possibly address this here. I can recommend a couple of websites that could help you if you want to find out what you're in for.
For AllData:
Here's the one for Mitchell as well:
If you want to find a speciaolist, here's a directory link for you: