Did not prepare for improvement do I go for it or not ?

I applied for coat accounting improvement which is tomorrow, and i js am planning to do theory but I heard just theory won't help , previously I had C grade , so will doing just theory work for improving even slightly ??

The problem is I have an exam the very next day in the morning and I did not even touch that subject even in the slightest bit, and i woukd have just 3 to 4 hours to prepare the whole subject ?

Can I just not attend the cost accounting improvement and retain my previous grade ??

If I score lower than before will my previous grade be retained ??

is theory enough ??

Do I go for the exam or not ? Does improvement even help?