How to go from a C to an A in Biology A-level aqa

Hi I'm 6 months in year 12 and I'm doing biology aqa alevel and I am struggling so much to do well. I keep getting B's and C's in my topic tests and I'm really worried for my exams at the end of this year cause it will be my predicted grades for uni and I would really like an A or a B. Any tips on how to do well in my tests would be really helpful