Question
when and how do you transplant a snowball bush?

Answer
Hi Sandra, Wait until you've had a frost, or the the plant has lost it's leaves for winter. On an old established plant, I'd dig the largest rootball I could handle.  If it's very large, I'd cut the plant back by 1/3 to 1/2. Dig your new hole no deeper, but twice as wide as the rootball and water it in thoroughly to settle soil around all the roots.  It will take about 2 growing seasons to re-establish a good root system, so you may need to give it additional water during periods of drought. Jim