When moving any tree, you should wait until it has gone dormant -- a time when root growth has slowed or stopped -- so the shock of the move is reduced. A good rule of thumb is to wait for the leaves to fall off or turn completely.
The first step is digging a root ball. A root ball is the network of roots and attached soil you see when the tree is lifted from the ground. To determine how large the root ball should be, measure the caliper or diameter of the trunk one foot off the ground and multiply that number by 10. The number you get is the diameter in inches of the root ball that should be dug. You'll want to dig down about half as deep as the width of the root ball. It's important to make sure the root ball is big enough to transplant successfully and small enough to stay intact and be moved.
When you are ready to replant, dig the new hole twice the size of the root ball. Place the roots in the hole and add enough soil to stabilize it and keep it straight; leave up to a third of the root ball above the ground. Water well and add a layer of mulch, which will help maintain the proper level of moisture.