To be able to delete the Store items no longer needed you must first delete the orders (after exporting the data) which contain these items from the system. You would need to either run a report so you have a copy of this information or go to:
  1. School Website > Content > Store
  2. Manage Orders
  3. Order Status: ALL and pull the information you want to save that way.

Two reports that may be helpful to find the orders containing the item are the "Order Detail-Exportable" that filters by date range or "Order Summary-by Product" that can be filtered by product, such as Adult Sizes - Crewneck - Dark Gray. You can find these reports under:
  1. School Website > Analysis > Reports  
  2. View All 
  3. Store category  
  4. Basic Reports subcategory