MacOS Mojave 10.14

I'm trying to download and install the MacOS Mojave 10.14 update so I can update to the newest version and some of my apps. I can download it but I keep getting the same message "This copy of the Install macOS Mojave application is damaged, and can‘t be used to install macOS." I've deleted the app, emptied trash and downloaded again 3 times now.

How I can get the update installed? Thank you for your help!