GCSEs aren't that important when looking at university courses (especially as you got a 6 in english and maths). I would look at courses you're interested in and just go through one by one with either a yes or no answer (you'll whittle them down quite quickly). If I was you, I wouldn't just focus on Manchester courses as you'll presumably still apply to 4 other universities. Does your school have a subscription to a website such as unifrog, in which you can put in your alevels and it suggests possible subject choices (there's probably some free websites you could use instead), which you could use as a starting point. The most important thing is to focus on what you actually want to do, but keep open-minded at first, unless you're deadset on something