Well, if your B was scored at a 75+ UMS, there's a fair chance for you to get an A if you work harder at your A2 modules and also a chance of making an A* though obviously it'll require one hell of an effort. As long as you take this seriously, revise daily (or weekly if daily isn't feasible) and practice a lot of past papers, you can achieve it. If your B was less than 75 UMS, obviously it is always possible to still score an A but it will be much, much harder.
So I suggest that unless you're sure you can study more seriously and devotedly then last year, you should repeat your exams if you have a 75+ UMS. If you have less than that then don't think too much and resit in your exams.
PS: I'm aware that some of the candidates don't know their UMS. In which case--I suggest you be the judge and see if you can study as hard as needed or not.
