How do I upgrade software

• If it is 10.6.8 - 10.13.6 then use the Mac App Store to check for updates.
• If it is 10.14.x or later then System Preferences - Software Update

NOTE: You will also need to let us know the year of the iMac as Jack-19 mentions, then we can tell you the latest version your particular machine can update to.

Hi chrisbeteau,

What model and year is your iMac? Go to the Apple Menu (top left) > About this Mac.

Cheers,

Jack