Hi n3qcr,
I would wait until next Spring before transplanting it. Do it right before it starts it's spring growth. Try to get as much of the root ball as you can. Since you didn't say how close they are, you might have to dig more depth than width to get a decent amount of the root ball. Try to have at least a 2 foot by 1 foot root ball. Be sure to keep it well watered after transplanting.
BTG

I agree. I moved one at that time last spring and it did great.

I'd move it in the fall. That way you won't have to wait until it sprouts to be sure where it is. It will already have stored up what it needs for the spring and can have the early fall to sink its roots in and be ready in the spring. I've actually moved some during the summer, but you really have to baby them to keep them going if you do that.