I just performed this repair on my 97 850, so the procedure should be similar.

1. Purchase the appropriate bulb (mine was PN 3524511 @ ~$6)
2. Pull the temperature control and fan speed knobs off their stems
3. Remove the visible Torx screws (2)
4. Using a small screwdriver or similar instrument, gently pry the square surrounding out, working each corner one at a time
5. Remove the square plastic panel (it's a snug fit)
6. Gently bend back the three tabs holding the printed circuit board and remove it
7. There are two bulbs - one toward the top center and one on the right. The bulbs must be twisted 90 degrees to be removed.

I couldn't confirm the bulb number or type prior to removal, so I left the dash partially disassembled as I brought the old bulb to the dealer to purchase the new one. Brentwood Volvo (St. Louis, MO) sells this bulb for $6.22, and my local dealer sells it for $11.20. Since I needed other parts as well, I ordered everything from Brentwood (have used them several times and remain pleased with prices and service).