Dropping one of your A2 subjects - will my school allow it?

I am attempting to drop one of my 3 A Levels: computing,as it was a bad A Level choice, and am going to go back to college next year to get my last A Level on a one year intensive. I haven't raised it with the school yet but I will soon. Will the school let me drop it and carry on with my remaining two A Levels? Can they stop me? (As is, is it their choice, or if my parents want me too do they have to let me do it?)

Thanks!