Installer link within Safari in El Capitan to upgrade to High Sierra is not launching the App Store.

I bought a mid 2011 Mac mini, and I replaced the hard drive with an SSD. Internet recovery installed Lion for me, so I then upgraded to El Capitan. Now, when I try to upgrade to High Sierra, which is the newest MacOS version that the computer supports, the link I click on that is supposed to launch the App Store just opens up an "App Store Preview" page for High Sierra and does absolutely nothing else. What am I doing wrong, and how can I complete this upgrade?