Changing Product Types

So I am trying to change product types of items so I can use the delete and change utility to merge items. I need to change some of the existing product types from finished good to kit, when I try to do so it says you cannot change the product type or kit when quantity or total warehouse values exists in one or more warehouses. Is there an easier way of doing this without removing quantity on hand and put it back in or will that ever work?

Could someone write me up a quick reference for merging prerequisites or point me to the help file for clarification.

Thanks in advance