Where is the air filter located?

Anyone know where the air filter is located on the R350? It's been a no brainer on other MBs.

the engine air filter is located in the top cover of the engine. just follow the plastic tubes the run from the radiator back.

Thanks, found it! Now.... how do I go about replacing the filters at home? It doesn't seem as simple as other Mercedes I've owned in the past. Seems like there are some sort of screws holding the housing and these screws are mounted from bottoms up. Would really appreciate your help.
 
BTW, how often do you recommend the air filter change?

Anyone that can help with this?  I''ve got the housing loose but can''t seem to get it out...any step by step instructions anyone can provide on the air filter housing removal?