Doddle really mate.
Get the front end loosened off - wheel out, forks out. undo top yoke, take that off, undo threaded collars, remove bottom yoke.
Now, assuming that you're using tapered bearings to put back in:
Using a drift, slowly tap the old cup out of the bottom of the headstock, and using a socket of the right size, tap the new one in (helps if you put it in the freezer overnight to contract). Same on the top. Biggest issue realy is getting the old bearing race off the stem, and fitting the new bearings to it - I generally ust give it to a mechanic mate of mine to sort to be honest. Then once that's on, stick it all back together!