Replacing would basically involve unbolting the broken pieces and reattaching the new part. You should have a torque wrench to get the bolts to the correct tightness. In general, you will have to slightly jack up one side or other of the back end of the car to get the new part to align the bolts with the holes. You may also have to remove a wheel.

If you have never done any of this, I highly recommend you have someone competent oversee the process. Working under a vehicle presents lots of dangers.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7