In my shared folder lots of files downloaded by itself

What specific files are you trying to delete?

if you come to this problem, maybe you can save your important files into a flash disk or U-disk, then reinstall your system and format your hard drive of the computer. you can scan your flash disk or u-disk using anti-virus software and delete potential virus.At last reimport the files to your computer,then everything will be ok.

6-8 GB space? Did you try to restore your system to date before those files got downloaded? Try it or you can choose scanning your pc too. You can also use some of the cleaning tools available to clean those unneccessary files.