Upgrading OS from Lion 10.7.5 on mac mini

Do you have access to another mac? Try and download high Sierra from the page jeffreythefrog mentioned and after that make a bootable usb device with macOS on it Create a bootable installer for macOS - Apple Support

you can find and download the older macOSes here: How to download macOS - Apple Support

the only issue I could foresee would be if you tried to upgrade past Mojave. as of Catalina, macOS became 64 bit only. I would recommend that you do upgrade to High Sierra. HFS+ to APFS should be fine. IMHO, I believe you should always run the most recent macOS that the Mac is compatible with.

gamera72 wrote:

Thank you frog and nick- the mini is now running El Capitan. I would like to go High Sierra next but I've read where Apple went to the APFS file system with that version. Should that be a concern moving from El Capitan to High Sierra?

Thanks, Don

We are running High Sierra on a 2011 iMac formatted Macintosh HFS+ without issues. Only if you want to change the mech hard drive for a solid-state drive (SSD) is the change in drive format to APFS recommended.

You can upgrade from Lion to macOS El Capitan in one leap, but High Sierra requires that you are already running macOS Mountain Lion (10.8) or later. That means two upgrades: 1) El Capitan and 2) High Sierra. Then you are done.

Back up your Lion installation to Time Machine and don't reuse that drive on later operating systems. The other issue is that some of your third-party applications may need updating and printer/scanners may or may not have vendor driver updates for the later releases of macOS. Even with High Sierra, your Safari will be far out of date security wise and you will need Firefox or Brave browser versions to resolve those security issues.

High Sierra does not offer a production APFS filesystem, so it will be HFS+ Journaled. If your SanDisk is formatted APFS, then High Sierra may not be able to recognize it.