I own a 2002 A6 Quattro 3.0. The check engine light is on, with OBDII code P0050 "HO2S Bank 2, sensor 1". I believe this is the O2 sensor upstream from the cat, on the driver's side. From the engine bay, I can see the sensor, but a lot of stuff is in the way, including the brake fluid reservoir. Can someone please advise me on a replacement procedure for this item? Specifically, should I approach the sensor from above (via the engine bay), of from below (under the car)? Any additional "gotchas" involved in the replacement?

Thanks. Brian