upgrading from 5.0 to 5.x

Hi - we just received two machines with RedHat 5.0 with a
year subscription and would like to upgrade those to the
latest versions of Redhat 5.x.

In addition, we have handful of machines running CentOS 5.0
and would like upgrade those to the latest version of
CentOS 5.x too.

Once I have yum running on RedHat, I'm presuming the upgrade 
procedure is same for both.

Is it possible to upgrade from Redhat/Centos 5.0 to the lastest
release of Redhat/CentOS 5.x using yum?

Any help would be appreciated.

Thank you.

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