How do you change the oxygen sensor on a 1994 Chevrolet S10 4wd 43 liter W?

Raise truck and secure. Slide under behind the passenger front tire. Locate exhaust pipe (Y-pipe). On the top side of the pipe you will see it pointing upwards. Un-plug it. Using the correct size (7/8" I think) and type of wrench or socket, remove and replace. Plug wire in.