[CentOS] Moving the system from 5.3 to 5.4

Tue Jan 19 19:41:55 UTC 2010
Renato Botelho <rbgarga at gmail.com>

Hello,

I built a system based on centos 5.3, now i'm planing to move to 5.4.
To do it I rebuilt all rpms making some changes.

When I use a common centos 5.3, it automatically detects that 5.4
is available and move update for it when i run yum update. How
does this work? How the system detects new version and update
for it?

I thought centos-release rpm just update repo for it, but I saw this
is not the case.

Could someone gimme some light?

Thanks
-- 
Renato Botelho