Where is the 02 sensor on a 97 c280 benz and how to change it?

All o2 sensors are located on the exhaust system, usually with in a few inches of the exhaust manifolds if its a 4 cylinder should have one six or eight cylinder could have 2 one on each side or one where the two pipes meet into a one. The sensors are hard to miss they look like a spark plug with one wire coming out of it. On the exhaust system most likely you can use a wrench to loosen it but some required a 02 sensor socket you can get at most any automotive part store, for around ten bucks Bryan ASE master certified mechanic.