I've had this hibiscus for 15-20 years and I really need help pruning it back - or maybe just the reassurance that I should prune it back hard. It has some sturdy trucks with new shoots, but the flowering branches are thin and arching out everywhere. The plant has lost it's structure and form.

Can someone help me prune it in the right way so it doesn't grow back leggy? Can I prune it back to a main trunk if there's no new shoots or leaves on that main trunk? Here's pictures: