I'm not sure what part your describing, but if you want to remove the pillar covering here's a brief from the cd manual. Remove 2 screws at bottom of pillar and seat belt bolt [all might have plastic cover caps]. Remove center strip by pulling toward car center. There's a clip at top of strip, so I'd use a downward motion. Be patient, or you'll break someting.
A good MB dealer parts dept will print out the parts diagram for you.
Best source for replacement is parts.com.
Bob