Hi stephencM,
I appreciate you reaching out to us here. Deleting historical transactions can have a negative impact on other areas of your books. For this reason, I recommend speaking with an accounting professional for their expertise and best course of action. If you don't have an accountant, we can help you locate a ProAdvisor in your local area. However, I see that you have reached out on another Community thread and I have also responded there.
See original post.
If any other questions come to mind, reach out again. We are always glad to help!