You cannot delete files, since they may be used elsewhere. The system cleans them up after a period of time....
There is a Private file tab visible in the file picker, if the admin has enabled it under Settings > Site administration > Plugins > Repositories > Manage repositories. If this is the case then a user...
Anyone enrolled in a course area where the file is displayed can access that file. Anyone with editing access in a course area where the file is dispalyed can link to that file in turn. If you want t...