The stem connects the handlebars to the...? If this is a stem... ... what's this?
I'm asking because I need to buy a taller one so I don't have to bend over as far. It's not convenient to buy a new bike, and I already have an adjustable stem which just doesn't quite get me there.
That's the fork steerer.
The fork has to be replaced if you want it taller. That, or perhaps, you could add another spacer to gain a marginal 10/20mm.... Replace the forks if you're desperate. 

Once you unbolt the stem, the forks can just drop out if you're not careful. Replacing the forks may not be economical to replace, and if so, I'd replace the whole bike. Good luck. :)

Actually, having said that, the steerer is already ridiculously high; I'd recommend time to replace the whole frameset, as making it too high can be dangerous, if not deadly depending on when and how it breaks. If you're going downhill and the steerer snaps from being too high and too much force going through it, it can shatter or snap, and if you fall on that, it will seriously injure you, if not killing you. Replace the frameset rather than just the forks. The whole bike looks too small for you.