Need to find location of oxygen sensor

The oxygen sensors are all on the exhaust system. There should be one on each side of the engine (front and rear, that is) and one more downstream sensor just a little past the catalytic converter, but before the muffler. Changing them is simple, really. You will need either a 7/8' wrench or a ratchet with a oxygen sensor socket (also 7/8'). Just take one out and put the new one in.

These diagrams may help.