Can I update OS X Yosemite 10.10.5, and if so how do I do this?

Back up your data in case something goes wrong --> Back up your Mac with Time Machine - https://support.apple.com/HT201250

Check if your old apps will still work with with the OS you want to install - https://roaringapps.com/apps This is particularly critical if you are upgrading to Catalina or newer.

Discover:

How to get old versions of macOS - https://support.apple.com/HT211683

• This link also has links to system requirements for each OS version which you should check against your exact computer model.
• You may find you need to use Safari to get the download links to open the page in the Mac App Store application.

You may also wish to note terminology. Software update, upgrade--what's the difference? - http://support.apple.com/kb/HT1444 [No longer directs to a document discussing this but basically an upgrade is a major system release such as replacing OS 10.10 with 10.11, and an update is a minor release for a particular system, such as taking 10.4.8 to 10.4.11. Software Update will check for updates but not necessarily for upgrades, particularly if a newer system will not run on an older piece of hardware.] Software Update looks for just that; updates, not upgrades.

Click on the link for it in the last article Limnos referenced.

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