Digging up a Japanese Maple. How?

I have a small Japanese Maple about 2'6" high with about a 3'6" spread. I would like to move it to a large container. Any advice about how to go about this? Is there a good time? How large is the root ball going to be and how sensitive are the things?

 

hi ...glad you reminded me, I got 1 about 30" am going to move it toady, it's overcrowded with other plants, will also put it in a pot for the time being. Better now then never, in my case ...or it never be seen orwill die anyway.Wold have been better in Autumn, but .....now is as good as anytime. Will reward me and make up for getting a better place, lol.
If you can take plenty of soil with it, should do no harm, I have even moved Roses in flower,they never stopped flowering, in fact the opposite,books are not always right, lol