Exchange Add-Ons: Switch Product Types
The Switch Product Types add-on allows you to change the product type after you have created the product. So if you created a product as a Digital Download but want it to be the Simple Product type, you won't need to recreate the product.
With the Switch Product Types add-on enabled (and both product types enabled), you will see the Product Type option in the advanced options of your product.
Simply select the product type you'd wish your product to be and then update the product.