You have 2 O2 sensors in your car- 1 in the exhaust manifold, and 1 in the catalytic converter.
O2 sensor in exhaust manifold location- accessible by simply opening the hood- exhaust manifold is located on left side of engine(part of engine facing the radiator):
To remove the O2 sensor in the exhaust manifold, remove the heat shield, disconnect O2 sensor harness connector, then use an O2 sensor socket to remove the sensor:
special O2 socket(available at any parts store):
The O2 sensor in the converter is accessible by jacking the front end of the car up and crawling underneath it -converter is located on exhaust system going down center of vehicle at end of engine compartment :
Disconnect sensor and use sensor socket to remove the sensor: