Install StoreFront 2.6 from the Command Line
Usually I am no friend of non-automated installations. You can see the command-line that is necessary to do a silent installation of StoreFront. The same command-line should apply for an upgrade from an earlier version of StoreFront (Please always test in a test stage before applying in production).
CitrixStoreFront-x64.exe [-silent] [-INSTALLDIR installationlocation] [-WINDOWS_CLIENT filelocation\filename.exe] [-MAC_CLIENT filelocation\filename.dmg]