How to change a Non-Stock Item to a Stock Item

We are new to Acumatica and would like to know how to change a Non-Stock Item into a Stock item.  Have attempted to delete the item and re-enter but cannot delete due to the item stating it is in multiple tables.  Have changed the posting class and still cannot change the item to a stock item.  Have attempted to fix the issue via Bills of Materials to to avail.  Thanks in advance for any information you can provide to help correct the issue.