Were it in my garden, I'd be ruthless - I'd wrench it out of the ground, cut back the top and replant in a larger tub, but preferably in the ground itself, keeping it well watered till it recovered, and this time, stand the pot on pot feet or something so that its not in contact with the ground. You'd need to remove at least a third of the topgrowth, if not half, to give it a good chance. You were always going to get to the point where this plant needed to be transplanted to the ground or a big pot because it became stunted - its only not stunted because it's accessed the soil beneath. It eventually gets to about 10 feet with a spread of 15 feet - you may feel that's not the right spot for it anyway.
This isn't an incredibly expensive plant to buy, so if it doesn't make it, you can always buy another one - and not make the same mistake of putting the pot somewhere roots can go down into the soil.