What's you end objective with this? Upgrading to XT/XTR won't give you significantly better shifting, and could give you a worse choice of gearing, these groupsets are designed for racing, not cruising, from what you have said, probably all you need is a new front mech, chain, cassette and cables an the drivetrain will be back to it's original condition.

If you intend you keep your current brakes, are you shifters brakes levers separate, if not, you need to budget for brake levers as well as new shifters.

What type of rear wheel do you have, if freewheel, you will need a new one if you are looking to go to XT/XTR, if freehub, the cassette is just a swap. For your front mech, you need to ID if it is a top or bottom pull &, the clamp diameter / fitting.