Safe/easy way to upgrade to Mojave on HP 8300?

I have a HP Compaq Elite 8300 SFF with High Sierra 10.13.1 running fine and smooth.

Just wondering

• is there any issues running Mojave and if there's an easy way to upgrade
• Is there a way to upgrade to Mojave without a fresh install?
• I can't see any macOS updates in the app store but i found this manual download of it here would that work?

thanks!