Use this if you are wanting to upgrade from a kit you already have! For example if you have the $10 gather kit, you can pay $15 more and get upgraded to the $25. You would lose your Gather kit in the process of course.
First things first, click on the server you have your kit on below. Then from there, click the on the Upgrade Kit on that page. If you are upgrading from, for example, the $25 kit to the $50 kit. Just click the “Buy Now” button, after that you will see an option to change the price from the default $15 to $25!