I'm not sure when they changed to 4 on all wranglers but my '99 had two, my '06 has 4. Anyhow, if you have 2 the upstream is at the exhaust just below the steering area driver's side at the exhaust, the plug is above by the steering shaft area. The downstream is back by the rear axle in the exhaust on the passenger side. I used an o2 sensor socket ($3 at harbor freight if you want a cheap one) but you can get them with wrenches too. Unplug, unscrew, replace. I followed the torque specs myself. Be sure to use the right one for the location.