On the page that loads after choosing "Additional Downloads" from the link you posted you have to click the upgrade link in the row displaying your device serial number. This brings you to a warning page about downloading and subsequently the order details page after you've clicked through.
In the product description section, click the 3 horizontal bars off to the right side and select "product list" from the pop-out menu. This should take you to the AM 8.2 section where you can then grab the upgrade package or ISOs under the files tab.
I'm half writing this so I remember where to find it next time, too. It's buried for sure.
