For financial reasons i'd say as soon as possible. Whether you drop out now or at the end of the year, if you know that you've made the wrong choice of course then I don't think universities will look badly upon you for doing something about it. It happens.
I do have experience of this. Although I didn't decide to drop out until the end of the first year. When I reapplied I never even mentioned that i'd been at university the year before, so I don't know whether they knew or not.