Hello Clint S ,

this is a great question. As long as you haven't yet started using the non-stock product in any transaction, you can simply select the item from your Product and Services tab, and select the EDIT button. From there you can change many details on the item, including the type from non-stock to service, etc.

But once any item has been added to an invoice, or used on any other transaction, you cannot change it from one type to another. 

What you can do is mark it as inactive, and simply create another one in the correct type.

I hope this answers your question, if you still more clarification, please contact our support team through the live chat, and we can walk you through this process.