The part number for the bulb and the holder is STC1983.
Remove the ashtray and the cruise control switch pack.
Remove the 2 screws on each side which will release the cup holder assembly.
Now you'll be able to reach the clock from the back and push it out.
Change bulb and put everything back the way it was.
You can also use some putty knife to release the locking pins that hold the clock. This is a much faster way.
Or you can go this route..... *********
When my '97 Disco's clock lamp burned out, I was told by the dealer that I had to replace the whole assembly (bulb + bulb holder), and it was somewhere between $7-$10.
I am, lets say frugle, so I set out to find another solution, and here's what I came up with. If you have 15 minutes to kill, it'll save you anywhere from $12-$15 (if you include the next time the clock lamp burns out):
1) Go to the local auto parts store and buy these bulbs, which are a direct replacement for the OEM bulb: Sylvania European Lamps part no. 2721 (W2, 1W). They were about $2 and you get two.
2) Remove the bulb holder assembly from the clock. If you look at the bulb holder assembly, you'll notice that the bulb leads are soldered to the holder itself.
3) Remove the bulb from the holder, either by un-soldering it, or by using a pair of pliers to pull the bulb out of the holder. If you do this, the part of the leads that are soldered will remain behind.
4) Remove the two side clips from the plastic holder. Do this by pushing the indented part (which holds the clip into place) of the clip in with a small screwdriver and at the same time pulling up on the clip.
5) Now either a) bend the leads on the new bulb around the metal clips from the holder and solder them on, or b) just wrap them around the metal clip.
6) Push the indented part of the clip back out so that when you slip it back into the plastic holder, they will snap into place. Snap the two clips back into place.
7) Install new bulb holder into clock, and your clock will come back to life.