To update everything just type the command, as root
yum -y update [a-z]*
And then to install everything extra available in repositories, command as root
yum -y install [a-z]*
Warning : It will download a whole lotta MBs or perhaps 1-2 GBs or more from repos with this method and make FC5 fully updated and equipped.
It shud update to all functionalities of FC6, but not so sure.