2002 f150 rear end

hi, i just bought a 2002 f150 i noticed there was a bit of a whine to it so i got a mechanic to test drive it and he thought it was the rear pinion bearing? wat does it take to change the bearings?

Replacing the pinion bearing(s) would basically involve rebuilding the rear end as it has to come apart to replace the bearing(s) and would be foolish not to rebuild it while you have it apart .