I change mine on a '02 Outback, although I would recommend good mechanics type gloves, and an open end wrench, I forget the size. You might have to run the engine to heat up the cats and expand the metal a bit... but it was real easy.
unplug the wiring, unscrew the sensor, the new one should come with some loc-tite(ish) material on it already, screw it in and pluc it back in. and have someone reset the computer codes.
good luck.