Hey vikas

Improvement exams basically aapke board exams k baad honge and you have to apply only when you are not satisfied with any of subject number. Suppose you got 40 marks in science subject let's say and you think that you can get even more then just go the improvement exam. And if in improvement exam you fails then it have nothing to do with your result.

For giving improvement exam you can go to the official website and can register yourself there.

Hope it helps!