gamerstation151: I'm new to GOG. How do I know which patches are installed for a game and how do I install new ones. Like where do I place them in the game folder?
If you're having trouble with the automatic download through GOG Galaxy, select 'Account->Library' from any page on GoG.com, you from there you should find The Witcher 3 in your library, click on it and select downloads. Here you can download all the patches manually and install them manually.
From the GOG Galaxy application, you can basically find the patch in the same place under The Witcher 3, click the more drop down and you should find the downloads for it there. This will be a slightly more automated process than downloading from the webpage.
If you're running steam version, i'm not sure if these manual patch installs will work, but steam should patch it automagically.