Just did that job the other day.
Un plug the sensor wire under passenger carpet, attach a string to the lead so you have something to pull the new lead through with, then push it thru. the floor so it is outside the car. The wire needs to rotate with the 02 sensor as you unscrew it or it keeps winding itself back into its threads as the wire trys to uncoil itself. I found it easier to thread the wire connector through the ring end of the wrench (22mm) and loosening from the passenger side of the exhaust. My wrench has a slight angle to it and I was able to get a good purchase on the 02 sensor. Once its out replace with new 02 sensor after attaching the pull string to the leads. Once the cable enters the car the rubber grommet can be fed into the hole.
This explanaition was too long but I hope you gat the idea.

Michael