How do you replace the oxygen sensor on a 1999 Oldsmobile Intrigue 3.5?

It screws into the exhaust near the manifold. I haven't had to change mine on my intrigue, but if it's like others I've had to change, you get to it under the car behind the engine. Follow the exhaust from the catalytic converter up to the manifold, it should be the only sensor with a wire coming out of it that is screwed into the exhaust pipe. Unplug it from the wire harness, then unscrew it using a flat wrench. Have a new one ready to install, you can't run the car without it. Hope this helps.