I would wait until it goes dormant since it will be less stress. Depending on where you are, that could be sometime in the Fall or Winter. Dig the new hole first. Then get as much of the unbroken rootball and roots as you can. You can also transplant it closer to Spring but in places where the soil freezes in Winter, that may be a pain and impossible. Keep the soil in the new location well mulched & as evenly moist as you can. Basically, treat it as if you had just planted it for the first time.