We have moved the help files to the web but the upgrade.htm document is not moved to the web so that's why it reported a 404 error.
You can find your upgrade.htm document from the local folder:
C:\TRiLOGI\TL6\public\Help\upgrade.htm
We have fixed this issue with the next release of i-TRiLOGI so in future when you select "Upgrade TRiLOGI" it will fetch the upgrade.htm from the local folder instead from the website.