Mavericks to High Sierra

I decided to finally upgrade my iMac from an old OS to High Sierra. I got as far as Mavericks, which appears to be running. However, I'd like to go all the way to High Sierra. When I go to the App Store, under Updates Installed in the Last 30 Days, it says macOS High Sierra. However, when I check the OS version under About this Mac, it says 10.9.5. How do I actually get High Sierra to be the OS? Thanks.