ficus bonsai yellow leaves

Repot a Ficus bonsai in winter?
I live in Wisconsin, and we're in the middle of winter to pass. Would I Be OK repotting my ficus (ginseng) bonsai? The roots begin to emerge from the ground and it becomes difficult to say how the soil is moist. Some leaves on the bottom of the tree turn yellow and die, which does not happen in summer. I have never re-tree, a pot before, so if anyone wants help with the procedure, I would appreciate it. For now it is in a deep pot (3 inches deep) and the new 2.5 pot bonsai. "How many should I root Trim? I also heard I should leave out of direct sunlight for a while after.
It's OK in the pan tropical weather all year, and a ficus is tropical. Looks like you're on the right track with a plant that has become rootbound will not hold water, causing the leaves to brown and fall. I potting tips on my site www.american bonsai.com – the Bonsai Care page. If you have any questions, you are welcome to me contact wchoat@american-bonsai.com. Also, I am pleased to send you specific care instructions for ginseng Fig.