Need to upgrade my iMac 2015 10.10.5 OS to 10.14

If you have a 2015 iMac simply use Software Update (System Preferences - Software Update) to upgrade to the most current version of Mac OS Big Sur.

Download Mojave from the second link den.thed posted.

rkaufmann87: There isn't a Software Update pane in High Sierra and earlier.

(204460)

See > https://support.apple.com/en-us/HT211683

For Mojave click on > macOS Mojave 10.14 using Safari.