Follow below steps to upgrade the Symantec installation Manager (SIM) offline to 8.0.79 version:
On the internet facing Symantec Management Platform (SMP) Server open the SIM and update it’s version to 8.0.79.
Download the Microsoft .NET Framework 4.5.1 offline Installer from https://www.microsoft.com/en-us/download/details.aspx?id=40779 and install it on the non-internet facing SMP Server.
On the internet facing SMP Server go to the following default location ‘C:\Program Files\Altiris\Symantec Installation Manager\Installs\Altiris’.
Verify the version of ‘symantecinstallationmanagersetup.exe’ file (from file > properties > details, it should be 8.0.79).
Copy the ‘symantecinstallationmanagersetup.exe’ (which 8.0.79) file to the non-internet facing SMP Server.
Run the installer onto the same directory where the ‘Altiris’ directory is already present.
After the installation is completed successfully, open the SIM and go to Settings > click on ‘About Symantec Installation Manager’ to verify the updated 8.0.79 version.