How to delete Unused Images?
Try audit Files module 


  Audit files is designed to perform audits of your upload directory and
  the corresponding database records. It will cross check that all files
  in the database have a corresponding physical file, or it will check
  that all files in the upload directory have a corresponding entry in
  the database.
  
  This module can be helpful in identifying orphan files that have not
  been deleted when their corresponding node was removed.
  
  The module has configurable options to ignore specified files and/or
  directories.
  
  The reports allow you to permanently remove files or database entries
  that represent orphans.