FC 17 delete large from but not free up disk space

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http://forums.fedoraforum.org – HI I have a FC 17 daul boot with win7 I tried to delete 4G Image file which was located in my NTFS disk by right clicking on it and deleteing it in fedora. it disapear but disk space left the same as before How can I return my lost space? Thanks (HowTos)