Simply go to the above link, or log into your JVZoo account and click on "My Purchases". On that page you will see a list of all the products you have purchased through JVZoo - including the product (and any upgrades) that you purchased.
Click the "VIEW DETAILS" button next to the product you wish to download.
Then on the next page you will see another button that says "ACCESS YOUR PURCHASE".
Click the "ACCESS YOUR PURCHASE" button, then you will arrive on a page with the actual download links for the files.