@jamie don't take this as super pro advice, but I did take a course on repotting, so hopefully my teacher knew what he was talking about. Here's what he said. (This was not about ficus, so YMMV): first, remove from the old pot. Remove as much of the old soil as you can, gently massaging the roots with clean hands. You want to replace as much soil as you can, so get as much of the old stuff out as possible without damaging the roots too much. Next, you can trim the roots if they're too large. >

@jamie I don't know how to judge this but you can probably find out. Once you're ready to put your bonsai in a new pot, you may need a few pieces of copper wire on hand to pin down some large roots so the tree doesn't tip over as you're working. If the bottom has large holes for drainage, you can place mesh squares over these, and gently pin down the roots (not tightly) through holes in the mesh, leaving plenty of space for drainage. Spread tbe roots out as much as you can so they will >

@jamie all have plenty of access to water and fertilizer. Next, add the soil. There are plenty of premixed bonsai soils available. You will want a smooth chopstick with a fine tip so you can gently pack the soil into the roots to stabilize your bonsai and make sure there is soil between as many of the roots as possible. It will help support the plant and also deliver nutrients. Be gentle, but don't be too delicate. You want the plant to be stable. Take your time with this step. >