How do you change the downstream oxygen sensor in a 2003 saturn ion?

Downstream O2 sensor is the O2 sensor after the Catalytic converter. Jack the car off the ground so you can get under it, disconnect the wire leads and with a close end wrench. Snake the wire leads through and wrench and place the wrench one the O2 sensor and with a hammer, tap the wrench to break lose the O2 sensor from the exhaust pipe. Once the O2 sensor has loosen up, just remove and install the new O2 sensor. Reconnect the wire leads, start the car and listen for any exhaust leaks. Once no leak has been determined, Place car back on the ground and go for test drive. Check engine light should go off after three start up and car has reached it's operating temperature and DTC codes will be erased after 100start cycle. Good luck and be safe.