I tried the demo, and the installer for that is called GSBDemoInstaller.exe.
Then I bought the collector’s edition, called GSBCollectorsInstaller.exe.
So look in your downloads folder or anywhere else you stash things like that, for .exe files that start with GSB and include the word Installer.
Hope that helps.
Edit: I just remembered that if you have an old installer (prior to 1.45) you will need to download the whole installer again anyway, because the patches won’t work for you… you will be missing things like the shield support beam and stuff.
So hunt in your email for a message from email@example.com with download instructions and fetch the full installer from the website.