I beleive you have a dust filter (1 large) and the typical carbon activated filters (2 small).
They are #540 & 310 respectively.
On my W210 the dust filter (commonly called cabin fitler) is accessed by removeing the glove box. The carbon filters are accessed by removing the decorative panel above the passengers knee space. Both are held in place by a simple clip system and when the door is remvoe the filters just slide out..
The carbon activated filter appears to be located in the same place as the W210.
http://www.detali.ru/cat/oem_mb2.asp?TP=1&F=211226&M=648%2E961&GA=722%2E626&CT=F&cat=64V&SID=83&SGR=045&SGN=01