High Sierra installer on imac.
I'm needing to upgrade from el capitan to high sierra on a mid 10 imac. I was following directions in a thread on this site but when I used the safari browser to get to the app store and hit 'open' to download the installer I get a message that says:
This copy of the Install macOS High Sierra.app application is damaged, and can’t be used to install macOS.
I'd appreciate any help in fixing this and getting me to an install so I can get back to work on my computer. I see other places claiming to have a copy to download but am nervous about using them.
Thanks
iMac 21.5″, OS X 10.11