You can manually install the OBS by downloading the upgrade pack (obs-win.zip) and do the followings:

1 Create the directory C:\Program Files\Offsite Backup Server
2 Unzip obs-win.zip to C:\Program Files\Offsite Backup Server
3 Run C:\Program Files\Offsite Backup Server\bin\install-service.bat
4 Open your browser and point to http://localhost/ (if you cannot see the welcome page, please check if port 80 and 443 are available. You can look at the log files available in C:\Program Files\Offsite Backup Server\logs for more information)