[CentOS] Upgrading from CentOS 5.6 to 6.0

Help!

Just ran the installation DVD but there is no option to 'upgrade'. Looked at
the RHEL docs,
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Installati
on_Guide/ch-guimode-x86.html#id4594292 referenced off the CentOS Release
notes but the CentOS installation doesn't offer the 'upgrade'.

I use to be able to upgrade by doing a 'yum update'. That doesn't work
either.

Guess I'm stuck with 5.6 as I an not about to install a new version and have
to rebuild all non-rpm packages from scratch. This is worse than Microsoft!!