Once your account is set up, unfortunately products CANNOT be deleted. They can only made inactive.
To change a product's status, use the drop down action menu in the product details page for the item you wish to deactivate. Chose
Alternatively, you can also deactivate multiple products using the import products function. Simply create a two column spreadsheet with the product IDs in column A and the Status in Column B (as shown below). Import this using the import products upload.
Please watch the 3:00 mark of tutorial video how to bulk deactivate products using the product import upload.