If you no longer sell a specific product, you can easily delete it from your Inventory. However, if the product is out of stock or you wish to prevent people from seeing it temporarily, you can simply hide it. For more info on how to do that, please check this tutorial.
To permanently delete a product, simply go to Inventory,
Click on the product you wish to remove, then scroll down to the bottom of the page (right under Visibility) and click on Delete,
A confirmation window will come up, warning you that this cannot be reversed. Click on Delete again, and you’re done.