If you are changing gears, you sure do need to take it to a shop,
unless you have all the special tools to set pinion depth,
and a press to remove the inside bearing from the pinion,
and a good selection of shims for both the diff main bearings,
and the pinion shaft.
My local Toyota dealer does it for $100 if..........
I just bring him the housing, with the rear cover off,
and somewhat cleaned out, and the side flanges pulled.
Plus the new parts of course.
It takes me less than an hour to drop the thing out of the car.
22 bolts/nuts to remove.
4 drive shaft bolts, 12 half shaft nuts,
and 6 mounting bolts on the housing it's self.
You need a buddy, a floor jack, and jack stands.
Use the floor jack to let it down from under the car.
This is the 2-man part,
one to ballance it on the jack,
while the other contriols the jack.
While you have it out, be sure to replace all 3 seals.