@hectormaciasa1979 There are some download sites (usually Mega Download sites and anime sites) that will fetch your download to the file system folder like that for you first and then serve you up the download from there. This of course leaves behind the original in the "file system" folder. As said you can delete them and the whole "File System" folder if you want.
If you goto the URL opera://settings/content/all, you should be able to find out what site is using that storage and then clear the storage for that site to get rid of its file system objects. That way, you don't have to do it manually outside of Opera. Of course, if that doesn't work out, manually delete them.