to be honest since you're in AS I would just resit the module you did lowest in, if you go up in a remark it will only be a few marks, if you resat you would really nail that paper and get a great mark on it instead of having a marginally better one than you had before, cos remember, just getting it up a few marks will make a difference but because ALL the MARKS count to your final grade, not the grade itself, it's better just to resit and get a load of extra marks.