I downloaded Fedora 18 x86_64. I used the following command in terminal for fedup.
sudo fedup-cli --device /run/media/omid/Fedora\ 18\ x86_64 --debuglog=fedupdebug.log
then I got a "finished successfully" and the prompt should reboot.
I rebooted the system and selected "System Upgrade (Fedup)" in GRUB. It showed a Fedora logo but nothing happened.