Lynn, to remove the old skin use disk sander or mini grinder and carefully run the disk back and forth along the edge of the door. You are only going to grind thru the sheet metal that wraps around your door frame. Check the window opening area for a couple of spot welds, cut thru them with your grinder. The skin is also usually bonded to a reinforcement that is inside your door, you can pry the skin from that.
Once you get the main hunk of metal off your door you are going to remove the little strip of metal that is spot welded all around the inside edge of the frame. Use a small sharp chisel and take your time or just grind thru the spot welds and pull the strip off with a pair of pliers.
Clean up the inside edge of the door frame, remove only enough paint to tack weld your new skin and shoot some weld thru primer on that edge.
Take the door and turn it skin side up, I usually put some adhesive caulk on the door reinforcement this will work to bond the skin. Lay your new skin on, have a look at the fit. I usually clamp on a couple of small pairs of clamps to hold the skin while I start the hammer and dolly work to begin to fold the edge around the door frame. Use softeners on the outside of the skin to prevent damage. No need for excessive force while clamping. Start at the bottom of the panel with your dolly on the skin side of the door and begin to gently start to hammer the flange over the door frame...go slow...don't try to flatten it all at once...work your way back and forth along the door edge gradually rolling the flange in place. Don't hit the flange too hard or you'll end up with dents from the dolly block(I use a toe dolly). Once this edge is done start the other 2 edges, same technique...back and forth until the edge is complete. If you want you can "set" each door edge flange just in the middle of each side to hold the skin in place as well. After you have the hammer and dolly work done put the door back on the car and align it with the fender and quarter. If you need to you can move the skin with a flat bar. When you are sure it's where you want it you can begin to put some tack welds in place. You generally only need a few on each side.
Sand the inside edge of the flange and door frame and prime and put a thin bead of seam sealer (optional) around the edge of the skin.
That's the old way of doing it, Eastwood now has this tool.
Here's a youtube video as a guide as well.