I changed my O2 sensor not to long ago. I had access to a lift, which made access quite reasonable, although you could accomplish the same using jack stands at the rear lifting points. You have to remove the outer heat shield to gain access to the O2 sensor itself. I was able to remove the sensor without removing the wheel. I used a small adjustable wrench. I was fortunate that the sensor was not fused into the bung. I've read from others that you must be careful not to strip the O2 sensor. If it had been fused then I would definitely have had to have an appropriate wrench for the job.