ShopTab has a very easy to use reordering feature within the administration interface. This feature is available to all users.
On your "My Products" page, click on the "Change Order" and choose to make a change to your product or category order.
Once on each page, you can either drag and drop your products in the order you desire using the icon in the left column or edit the rank field by entry of the order you desire for that product.
All products in your store will appear on this page. Your changes will be immediately updated in your Facebook Store.
You may change the listing order of the categories in your Facebook Store drop down menu by editing the category order. These changes will not change the order of your listings on the My Product page.