Can I update macOS Sierra 10.12.6 to macOS High Sierra 10.13.6

Besides Niel's always great advice...

If you get a corrupted message...

Naw, not damaged, it's just that you have an old copy already in Applications, there are 2 cures...

Disconnect from the Internet & set the Date back to 2014, then you can run the Install MacsOS High Sierra App in Applications, so expired Certificates are not expired.

Or... trash the Install MacsOS High Sierra.app in Applications, empty trash & restart, then a new copy of a more recent version can be downloaded…

Don't use FireFox for this link, it’ll offer strange erroneous errors…

https://itunes.apple.com/us/app/macos-mojave/id1398502828?mt=12

Hi,

Go to the Apple Menu > About This Mac to see exactly which Mac you have, then find out if it is compatible with a newer OS here: How to get old versions of macOS - Apple Support

I get an error message by Clicking on the download link on App Store for High Sierra. " This copy of the Install macOS High Sierra application is damaged, and can‘t be used to install macOS."

Any advice would be helpful

Yes. Back up your data and check your applications for compatibility; the download link will be in the article tjk referenced.

No Mac model has a maximum OS of Sierra.

(216205)

Choose Applications from the Finder's Go menu, throw the existing installer away, and download it again.

(216705)

Thanks much Niel and BDaqua, finally got around doing it and trash install tool/fresh download worked fine

Great to hear, always like to hear the outcome, take care my friend!