You can transplant during the growing season. Late fall through wimter is best but Ive transplanted many a tree in the dead of summer. You gotta keep an eye on it and make sure it gets enough water, but not too much. Transplanting isn a whole lot different than planting in general.
Be sure when digging your rootball not to but off too many of those fibrous hair like roots on the end. Those are your feeder roots and they are the first to take root in the new location and get the acclimation process over with.