all O2 sensors are located in the H-pipe, they just screw in, if you look underneith you'll see wires comming from them on the pipes, most are easy to get to
On your car there are 4 O2 sensors. the first two are befor the first set of cats if you jack up the car they are right to the sides of the h pipe. Those stay there if you install a after market H or X pipe the ones befor the mufflers are the ones you put the mil eliminators on get the steeda eliminators they require no splicing they just clip up. And on new modles they are a B##ch to get to i got mine off on a lift to get the first two off the second set is simple.
So if I get the car jacked up I can get to them (front). As I understand, you just usually have to replace the 2 in front of the cats. Car has 76K miles and have a state emissions check comming up. I also want to be sure the engine is running tip top and I am getting the best possible mileage.
When I installed my new X-pipe I could not get my hand up in there to disconnect the wires for the front two sensors. I had to wate until I lowered the old H-pipe to get to the connectors. The connector on the rear two is the same. Practice on those to see how they disconnect. Find a friend with small hands. Good luck.