How do I upgrade my Mac Yosemite version?
How do I upgrade my Mac Desktop?
Current Pro Desktops
Open this Link How to get older version macOS and in following page decide the version of macOS the computer can upgrade to. Once decided click the link Using Only Safari as others will NOT function. Safari will open a redirect and open the Apple Site to desired version of macOS. Do verify Apps Compatibility before upgrading as Yosemite to whatever new version is a leap. And, perform a Time Machine Backup and have at least 1 TESTED Bootable Clone - insurance incase the upgrade goes sideways.