How can I change the oxygen censor 1?

How can I change the oxygen censor 1 of a Chevrolet Venture 98? It is found before the catalyst, just after multiple. For their Hubicacion 5 mechanics they tell me that they cannot remove it. How should it be removed?

The oxygen or LAMDA 1 probe sensor is found, in all vehicles, in the anterior part of the catalyst. The way to change is quite senzilla, unplugs and unscrew it with an English or similar key. The location of the probe in your vehicle is not a problem to disassemble it, it only brings a little more work, nothing complicated for a mechanic that really is.