In my experience, most people tend to go down from AS to A2.
However, with retakes and taking into account how close you were in your subjects, I would go as high as ABB.
A2 exams are harder, however, resits will be easier. I think if you want ABB it is going to be challenging but possible.
I went from AAAB - AAA from AS to A2.
However, My actually unit grades at A2 were lower than I got at AS.
Best of luck