I mean it depends what you want to do in the future. If your saying you want to scrap both History and English Literature for Business Studies, it seems like your choosing a completely different career plan. So you should align the subjects you plan to do with what you want to do in the future.
If you are planning to resit the subject you didn't well before, as you mentioned History coursework or English Literature written exams then you should go over the big mistakes and correct them and work on the weakness that was letting you down. Of course on top of this, you also got to revise and stay up to date with content, do past paper exams, ask for help from close friends you trust and know they are capable or from your teachers and utilise the internet.
I cannot comment on self teaching, since I never done it. It probably sounds self explanatory but I am probably not the best to take advice from that.
All the best.