Its easiest changed from under the car...All you need is a rachet with a long extension, and you can pick up an O2 sensor socket at any autoparts store. Its a special socket with a cut in the side to let the wires fit in the socket. They can be a bit stubborn to get out, but they usually come right out with a bit of grunt. And when you go to put a new one in, DON'T wipe off the silver grease on the threads, this is anti-seeze. It keeps it from getting stuck when it time to change it again. and that sensor by the oil filter is the oil pressure switch for the oil light on the dash.