1. Like me so many of you would have been waiting for the final release of Fedora 18 spherical cow...but at the same time when u see it released u have so many links to move around on how to upgrade from 17 to 18 but u keep ending up with previous one....i went through the same for past hour...:-)
2. The only set of commands Fedora 17(only) users need to put in are these :
Reach the Root first with the password ie
su -c 'rpm --import https://fedoraproject.org/static/DE7F38BD.txt'
su -c 'setenforce Permissive'
su -c 'yum update yum'
su -c 'yum clean all'
su -c 'yum --releasever=18 --disableplugin=presto distro-sync'
su -c 'rpm --rebuilddb', or rpm -qa will not work due to a upgrade of rpm
3. For me the upgrade is around 1.6 G as seen in the screen shot below :
4. Mine is upgrading on way....another few hours should be ok....:-) all the best for your upgrade