Upgrade iMac12,2 from Mac OS X 10.6.8 I have an iMac12,2 with Mac OS X 10.6.8. I want to upgrade to the newest possible Mac OS. If I click the Software update button it says "Software Update doesn't have any new software for your computer at this time.". If I want to download High Sierra from the App Store it says "This update requires macOS version 10.8 or later." 

What should I do? How can I upgrade my mac?
On Apple's How to Upgrade page it states 


  Upgrading from OS X Snow Leopard or Lion. If you're running Snow Leopard (10.6.8) or Lion (10.7) and your Mac supports macOS High Sierra, you will need to upgrade to El Capitan first.


You will have to first upgrade to El Capitan, then to High Sierra. You can follow these instructions to get El Capitan.