hadwood59: The file that I'm talking about is Galaxy Client which was placed on C drive and when check properties all the files come to 36 GB the file that says Games which has 35.9 Gb in it. I don't understand what to do about this. The C drive only has 9GB left.
It seems The Witcher 3 is installed on your C drive. Please contact support for technical info on how to move the game to another disk (although I don't know if it's in support's area of responsibility).
If it's an option for you - you can always uninstall TW3 and install it again on the other drive. Make sure you're not removing save files.
Don't worry about GOG Galaxy application at all - it will detect the game was removed from the folder it was in - and you can scan&import it from new location at any point. Just worry about moving your game properly.