I'd leave it alone, for the most part. Maybe if you move it to a different spot you will then no longer see it as overgrown.
I'm curious what others will say. There are some good tutorials online (Essence of the Tree has some on youtube) on how to prune upright JMs for shape and health. I actually think your tree is quite lovely and is growing into a good shape on its own. If anything, I'd perhaps trim out some of the interior branching so that the tree has better air flow. I'm new to this size of tree, however (most of mine are younger, only a couple of mine are the size of yours), so I would defer to those who have more JM experience.
