Editing a file is only possible if you have write permissions on the file.

To edit a file click on the action menu (which is accessible by clicking on the three dots on the right edge of a file entry) and select the action "Edit file". A dialog will open in which the name of the file, its description and its terms of use may be changed. After clicking the "Save" button at the bottom of the dialog all changes made to the file will be saved.