I believe the uppipe bolts can be removed without taking the O2 sensor out, but if you want to take it out, here's a way how. IIRC, that is a 22mm wrench.
http://img.photobucket.com/albums/v334/wcbjr/DSC00438.jpg
http://img.photobucket.com/albums/v334/wcbjr/DSC00440.jpg
http://img.photobucket.com/albums/v334/wcbjr/DSC00445.jpg