To delete PR which has Part Verification.

Hi expert, When I try to delete PR(Problem Report) which is connected to Part Verification, system doesn't allow it by showing message below: "PR cannot be deleted. It is used in Problem Verification parent_item. " and if I try to delete Problem Verification, system also doesn't allow it. "Problem Verification cannot be deleted. It is used in PR Problem Verification." In this case, I would like to delete not only PR but also Problem Verification too. Would you please help how to do it?   Thank you.