Hi alangill
You should have been sent a confirmation email that would have included the download link. If you didn't, then please use the following instructions to access the digital download and the serial number.
You can access digital download purchases by going into your order history, which can be found here: https://www.auran.com/planetauran/Order_History.php
Once on the order history page, click on the order number that matches the digital download purchase. On the order page, you will find a download link, click on this. This will take you to the download page, where you will find two download links. Please try using the top download link first.