I recently started using my iMac (2013) again after about a year of it being idle. I know that is needs updates, but when I go into the the app store to check for OS X updates it shows that there aren't any. It is currently stuck on version 10.10.5 OS X Yosemite. What can I do to update?
iMac Pro
The App Store Updates page only informs you of updates available for the OS you are running.
Installing a newer OS is called an upgrade.
An iMac from 2013 can upgrade to all OS's up to macOS Catalina.
As your mac can upgrade to the newer OS's like macOS Mojave 10.14 and macOS Catalina 10.15,
I would recommend you upgrade to macOS High Sierra 10.13 first.
For High Sierra, Mojave or Catalina,
Open Safari and click on this link,
How to get old versions of macOS – Apple Support
Go to Check Compatibility to see if your mac qualifies for the OS upgrade you want.
Then go to the Download OS section and click on the OS you want to install.
Before upgrading make a full back up of your Mac.
Check that third party apps you use have updates available for the new OS.
Check that your printers/ scanners etc have updated drivers and software available for the new OS.
Connect your mac to your router via cable rather than rely on WiFi.
Do not use your mac while it is downloading
and do not use any other devices that share the same internet connection.
If the App Store says ‘Open’ then it is detecting a previous download of the install app
go to the Applications folder locate Install macOS ******.app.
Move it to the Trash, empty the Trash.
Restart, click on the link again, the App Store should say ‘Get' or 'Download'.
If you are considering upgrading to Catalina be warned it does not support 32bit apps.
Your Mac is probably running 32bit apps and these will need to be updated to 64bit apps,
some updates may be free, some may be paid. Use this app to discover which apps you have
are 32bit, https://www.stclairsoft.com/Go64/ then contact the developers of the software to see
if they are offering 64bit updates.
The Age of this computer will Govern what newer version of macOS it will Qualify to install. Use About this Mac from the Apple Icon on Desktop - the required Information will be there.
With the above information in-hand - follow this How to get old versions of macOS and verify what version this computer Qualifies to install. Make sure to use Only Safari to commence the download as Others may not work
Make a Time Machine Backup Before attempting. Notation - Mojave is the Last version to support 32 bit applications / extensions and Drivers. Catalina Only support 64 bit and there is no workaround.
To check for 32 bit applications - Go64 is a Trusted Developer and help identify the 32 bit Applications.
Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation
the 2013 iMac can run macOS catalina and before. check your apps for compatibility with each of those and go to this link.
Mac OS X Won't Show Updates
