I just got a new rear cassette. It is a Shimano Ultegra CS6700 11-25T, which I want it to replace a similar cassette with 11-28T.

How difficult is it to replace the rear cassette? How long does it take? Anything I need to watch out for, like special lubricant, torque figures, washers, etc? Can I just take the wheel and cassette to my LBS and expect them to be able to perform the operation fairly quickly?

Thanks for the advice all.