Pull the cluster. I have the MB tools which makes it any easy job. They wedge in between the cluster and the dash, and grab onto some ridges on the cluster. Then you pull. Carefully and sternly at the same time.
Once out, replace ALL the bulbs so that you aren't doing it again next week. My dealer had the bulbs packaged as a set for about $25. For some reason the clock or temp display is always the first to go.
For a non-DIY alternative, most dealers charge an hour's labour.
1998 C230 "Black Betty"