Picea pungens yamadori repot needs advice

I won this in a raffle last October.  I want to repot it this spring, but don't know anything about spruce.






When can I repot, how much can I reduce the roots, and what should I look out for? Click on each image to expand the view.

Speak with your local bonsai adepts. Figure out who is knowledgeable . Treat this old collected tree carefully