I am getting an error "This copy of the Install macOS Mojave.app application is damaged, and can't be used to install macOS. I clicked on Mojave above. then clicked on "open" to get this error. How do I upgrade?
See above
iMac 27″, macOS 10.12
Don't use FireFox for this link…
https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12
If you get a corrupted message...
Naw, not damaged, it's just that you have an old copy already in Applications, Trash the Install MacsOS Mojave.app in Applications then a new copy can be downloaded.