Oh okay, so everytime i want to update GSX i have to download the installer from justflight again?
As I've said, as far as we know, the link contained in the receipt from Justflight it's just a link to our site so, you'll always download the installer from the FSDT site, not Justflight's.
This, assuming you need to download the full installer, which is not always the case.
Lots of updates can be applied just with the included Live Update feature, which notifies you of updates, and which contains release notes you can read, which might include additional instructions to apply the update. The latest two Live Updates, had a note that required you to download and install one of the GSX Vehicles updaters too.
But the full installer is always updated, so you can be sure it contains everything.