I am using moodle 2.4.1, can anyone help me with this?
There is no need to do anything, as any unused files are detected and then deleted automatically after a period of time. Users cannot delete files manually, since they may be used elsewhere. (Source: Repositories FAQ)
To expand on what Helen said, the files will go away on their own *as long as they are not linked to.*
If you have a folder full of videos but no resource or activity or forum, etc, links to them, they will go away.