How do you remove oxygen sensor from 1990 Toyota Celica ST?

First off use a spray lubricant very liberally on the threaded area of the sensor. (I recommend PB Blaster. It is a miracle in a can!) Secondly, cut the lead wire close to the sensor so you can use a socket on it. (preferably a 6 point to reduce the risk of rounding off the soft brass hex. Use 1/2" drive for leverage). when installing the new one use a crescent wrench. Do not over-tighten.

Mike