how to updatePickerView Data according to previous picker view selection

I have 2 pickerView. one is showing courses and other is showing courses sections according to courses id(Response is going from Json) now the problem is when I choose course(lets say calculus) and then select the sectionPickerView it gives me list of corresponding sections(A,B,C,D) but when I change the course again to (English) the section PickerView still shows the same section and doesn't update sections according to Course Pickerview.I have 2 pickerView. one is showing courses and