How  to upgrade  from Fedora 17 to to Fedora 18?
Before to start upgrade , please  backup any  critical data  before  to start  the upgrade
you can upgrade it by using fedup
1- install the latest version by :
yum --enablerepo=updates-testing install fedup
2- Now you can upgrade by using one of the two methods bellow:
2.1 – By using network
  sudo fedup-cli --network 18 --debuglog fedupdebug.log
2.2 – By using an iso file
Download the iso file to your pc then run command on terminalÂ
sudo fedup-cli --iso /home/user/fedora-18.iso --debuglog=fedupdebug.log
And is done.