how to change a upstream o2 senser on a 1999 chrysler sebring jx convertable

I believe the upstream O2 is the one on the end of your exhaust manifold directly from the engine. The other O2 sensor should be just before your catalytic converter on the pipe. All you need is an open end wrench to get if off. They do make a special head that will fit on your ratchet which makes it much easier to remove.