Air filter replacement

After getting a quote of $160.00 to replace the air filters in my 2000 SL500 I decided to get the parts and do it myself. The parts were $40.00 for two air filters. Now, does anyone know how to get to the air filters. I am unsure how to get the plastic cover off the top of the engine. It does not appear to be screwed on and cannot find snaps holding on eithier.
Some direction would be very helpful.

Thanks,

Keith

I gave you a post up in the nonspecific where you posted check it out if you haven't gotten it already.