https://fedoraproject.org/wiki/Upgrading_Fedora_using_yum#Fedora_18_-.3E_Fedora_19
Will see what the result gonna be …
version 18->19 no issues seen, only executed following
# yum install fedora-upgrade
# fedora-upgrade
version 19->20 some packages had dependency errors, yum remove <packaname> resolved the issue
# rpm –import https://fedoraproject.org/static/246110C1.txt
# yum update yum
# yum –releasever=20 distro-sync
