Riding position depends on different things, of which the bike is just one. The distance between the saddle and the handlebars combined with the the length of your body and your arms limits the options you've got.
But the kind of cycling you do is just as important. When riding around town, especially in crowded places and/or when not being in a hurry the best thing to do is to sit straight up. It allows you to make short turns, it's easier to stop, it's easier to look around you and allows you to talk to the person riding beside you. (With some practice you take you hands of the handlebars and still steer with just your balance and stand still on your bike without getting a foot on the ground). You need your saddle to be somewhat below your handlebars, but still at a height where you don't have to bend your knees to far. This basically is the way the Dutch cycle around town. It works when you treat cycling as an alternative to walking around instead of a sporting activity or a way to go fast. (Because, when moving around on your feet you're not running all the time either).
Judging from the image your bike seems suitable for that, the pedals seem to be slightly more forward then a road bike, which will push you a bit straighter up anyway.
If you want to go faster you can lean more forward, but depending on the length of your body that might get a bit cramped. If that's an issue you could but an armrest like this on the handlebars allowing you to lean further forward.