This could not be easier, just go the products category and choose from the dropdown select all products. A new screen with all your products should appear. Hover your mouse over the product that you want to change. Click the Trash button and you’re done.
Just remember to go and remove the image from the image gallery as indicated in the How to remove an old product image from the gallery in this guide. This is important as it can overload your disk space and cause you to spend more on hosting.