How to update a 2009 iMac using OS X 10.10.5
How to update a 2009 iMac using OS X 10.10.5
iMac, OS X 10.10
Question marked as
Early and Mid-2009 iMacs cannot be upgraded beyond El Capitan 10.11.6 and Late-2009 iMacs cannot be upgraded beyond High Sierra 10.13.6.
If yours isn't at the last possible upgrade as indicated above, see instructions in: How to get old versions of macOS - Apple Support