It won't be easy at all but it is very possible. No more fun in the common room!
Last year in edexcel biology I got a b in unit 1. And Ds in unit 2 and my coursework; which overall was a C.
Retook the D exam and this year got 118/120 = A
Redid my cow and got 37/40 = A
Worked my a** off at A2 and that I ended up with an A overall (5 ums off my bloody a* which I aim to achieve over the next year) but it is still far from my previous ugly C. Lol
All you need to do is retake the exams that let you down the most and calculate how these will allow you to achieve the necessary UCAS points for an A grade at AS and then this will make it easier to achieve the A at A2 because A2 is significantly harder.
In saying that once you start studying A2 AS becomes a lot easier to understand and your more likely to ace the exam.