You can cut it radically down, and you can take cuttings and start new plants. Jades are easy to grow and to propagate. The only thing to be aware of, is too much water, especially in winter.

Very nice sized jade although had you potted up over the years, I think it would be much larger. Definitely prune and prune hard. Do it soon. In the dead heat of summer, they slow their growth a bit, but I don't think you get as hot there as we do down here in Texas. Prune all of the thinner branches that are hanging of the edge of the pot to the point just below where they curve. The bigger, thicker branches, I would prune back to about three or four inches above where they V. Read some threads on rooting those cuttings and you'll have several more plants. I would definitely repot and make sure all of your heaviest branches are upright. You can take the whole plant out and losen the soil. When mine is being a pain, I often set my hose to shower and wash it off. I do the same with all the new plants I bring home to get off all the heavy soil they're grown in. You may have to cut some of the roots to separate the stems some or to get those leaning to be upright. It's okay. New roots will grow. I have seen these really cool supports at Home Depot used to support taller growing flowers or pepper plants. The smallest is 18" and they go all way up to 36". They are green and simply a long metal post that goes as far as you need it into the soil with an open circle at the top that is slightly bendable so that you can open it to put around the stem of your plant. In the end, if you used these to stake your branches, you would probably have to cut them off, but I think they'd work great. You could also use regular stakes and just tie them to the plant. Just make sure you check your ties to prevent them from cutting in. When you repot, wait a week or so before watering so that the roots have a chance to heal. This avoids rot.

Likewise, I wouldn't cut again without a clear reason to do so (rot). Let it callus a few days, re-pot in a dry coarse mix, then water in 1 - 2 weeks time - dribble some water around the stem, maybe a half inch out, without soaking the mix or hitting the cutting directly. Josh

My 5cents... 1. pot is too large, too deep 2. soil needs some 'lightening-up'; add generous amount of perlite if you can't get anything else (I use small grit a lot); research soils for succulents on this forum. If you see recommendation to add sand anywhere, I would say DON't, unless it is really gritty (larger particles) 3. rocks on the bottom/halfway up don't work, get rid of them. Get shallower pot AND well draining mix instead. 4. just because 'nothing is hanging' (sorry ez to contradict you), doesn't mean plant is healthy. You need to squeeze (gently) trunk and branches to see if they are too soft - but sometimes they are soft just from lack of water. I do not think that is the case with your plant - it started to rot for a reason. Water was, probably, getting poured (sometimes we don't notice) over same spot on trunk, perhaps there was a small injury that allowed water to get in - anything is possible. I would gently swish the root ball in the water, cut off roots that are mushy-slimy. Any black spots/areas in the trunk or branches you see on cut pieces are sign of rot spreading. Unless you get rid of them, it will continue to spread. Small and healthy piece is better - and will grow in proper conditions - than larger-longer sick one that will eventually die anyway. It is clear to me from the last photo that the branch is growing from the trunk/stump, so you can leave it. Not 100% sure, but 4th photo from the bottom seems to show some darker areas - double check on that. If yes, cut further. When you pot it up, don't bury trunk too deep, as long as the roots are covered, that is enough. You could put the rocks (ones you had on the bottom of the pot for 'drainage') on top of the soil around the plant to support it - how large are these rocks?