We have many clumps in our home gardens that have been undisturbed since 1989. However, if a hosta is not doing well in one location it sometimes helps to move it. In any event, hostas are best transplanted in the spring. We prefer to move them in the "bullet" stage....i.e., when the divisions are about an inch or two above ground and the leaves are still tightly wrapped. They should be replanted at the same depth they were growing in the old location. Obviously, you should try to preserve as much of the root system as you can. If you don't plan on dividing the clump, try to keep the root ball intact as you move it.
When transplanting, be sure to amend the soil. We prefer to add course construction sand and composted horse manure as we transplant. Adding compost when you transplant will give the plant a boost in its new location, and help in water retention.