I have never done 2003 model but I have never met a door panel I could not figure out.
First look for any screws.
ON Explorer's typically they are near the door open handle, just two screws.
Next remove any ash trays, the little trim piece around the door pull handle, etc
Roll the power window down
Get yourself a small flathead screwdriver
Work it between the door metal and the door panel down at the bottom.
Pry the door panel off carefully.
It is held to the door metal with plastic one time use clips often called x mas trees.
You will want to work the screw driver around the edge, getting next to each clip then pry to release it.
ONce all the clips are free you pull the bottom of the panel out, and then the top of it up, over the door lock button and free from the window seal.
Next hold the panel out from the door and unlip or unscrew any wiring connectors that go from the door to the door switches and puddle lights.
install is the reverse.
If it was a truck you were going to keep its advised to buy all new x mas tree clips, but typically they can be used two or three times if you are careful removing them
Takes all of 10 minutes once you have done a few of them.
Screwdriver is not the best tool, but it will work.
