Can't delete anything from the files folder#

My client has just told me that she can't delete anything from the files folder, because the delete button is grayed out. I have tried placing a 777 permission on all of the files, the delete button is still grayed out. Can someone please tell me some way I can enable her to delete the files?

have these files been uploaded via FTP or through the Manager?

The files have been uploaded via the Manager.