Updating to High Sierra

Hi! I'm trying to update my mid 2011 iMac from Sierra 10.12.6 to High Sierra 10.13. When I click on this link thru apple support https://support.apple.com/en-us/HT208969 it takes me to the app store which it then says I can't access because I dont have OS 10.6.6 or greater. Sigh...I tried my clicking on my App Store icon in my tool bar but High Sierra is not available. I also tried software updates via about this mac but there weren't any update options. Any other way for me to update? Thanks in advance for any help! 11/10/20