When you transplant a tree, you must disturb the root ball as little as possible. This means digging a line around the tree that is about as big around as the upper branches of the plant. You want to dig down and under the roots so you can remove the whole plant, the roots and all the soil around the roots all together. The plant sustains itself through very tiny roots that extend into the soil horizontally past the largest branches on the top of the plant. You want to take as many as possible without disturbing them.
The best time to transplant is in the fall, maybe next month, or later in the fall when the tree has lost it’s leaves.
Transplant to a place with good sun and good soil. Dig the hole for the new plant a day before you plan to transplant. Dig up the plant and move to the new hole as quickly as possible, exposing the roots to the air as briefly as possible.
Put good soil into the new hole and press in with your fingers until firm. Water well, but don’t make mush. The plant will probably droop from being transplanted. If there is strong sun, make something to shade the plant until it is looking peppy again.