If you are looking to make it fuller foliage-wise, you should just be able to prune the individual stems back and they will regrow new branches and foliage. I read they can be finicky in some regards, but apparently they take well to pruning.
Edited to add: just be mindful of your watering when you prune it back. Less foliage will mean less water intake, so if you water on a specific schedule, you will need to cut back just a little until you see it actively growing again.
