Starting Education over? From A- Level?

I am 24 . Living in Bangladesh and an undergraduate student in Chemical Engineering . It's been 6 years since I got admitted and I completed less than half of the credit hours required to complete graduation. I am not interested at all continuing in this subject . My interests lies in subjects like Mathematics ,Computer Science .I feel like wasting time . Since it's not possible to start undergraduation over again here , I am thinking about starting from A- Level . I need your suggestion can I take private courses on A-Level while continuing in current university or to go only with A-Level?