Retaking the class wont hurt you and it will help you in the long run. Why? because if you get more A's they still count as new credits and all your GPAs will go up. My friend retook a bunch of classes. Is it absolutely necessary? Not if your GPA is a 3.5 or above. Will it help? Most likely yes. But it also depends on if you have the time and money to do so.
Just dont retake if you have an A-. I would probably retake with a B-/B if i had the time.