AlainK
Imperial Masterpiece
welcome to the forum!
Ditto.
What derek7745 wrote is the best advice you can get.
Most of us I think would take option number 2, air-layer, but for a beginner, option number 3 is probably the best.
The tree doesn't seem root-bound, repotting it next spring woul be an option I think. Repotting is of of the basis of bonsai. There seems to be a lot of feeder roots above the red line, I would cut out all the roots below, even big ones, just before budbreak, and put it in a shallower pot/container with a "good" soil.