Gary, coincidentally I just signed up tonight as well, seeking help with my parking lights/marker lamps/brake lights. I just replaced one of the parking/turn signal lights last night in my 1990 Deville, and I imagine the process is very similar. Obvious, you can you lookup which light you need at your local auto parts store.
First off, to get a better look at where you are working, you may want to remove the side light(same level as headlight, but on side of car.) There were two torx screws holding these in on my 1990, one on the top of the light fixture and one on the bottom.
Now, to get to the parking lamp, you will need to lay under your car and reach up and around to the light fixture. On my car there are TWO parking lights per side, but they all look like one unit. You will need fairly small hands to reach up inside the fixture. Once you reach up inside the fixture, feel for the light. When you find where the light is inserted, grab it and twist it 1/4 turn counterclockwise(or clockwise is fine too I believe). After you turn the light, it should come out of the light housing. NOW, on my DeVille, I could NOT pull the light completely out to switch it out because the wires were snaked through a very small channel (The light was too big to pull through). What I had to do was pull back the wire sheathing and cut the tape so I had more slack in the wires. After I had more slack, the wires were long enough to pull the light through another small hole below the light fixture. Once the light was pulled out, I swapped out the bulb and did the above instructions in reverse.
This description is probably confusing as all get out, but it's the best I could do on short notice
Let me know if you need clarification.