Hi Fernando,
1. upgrade 5.5 to 5.6 (download the ISO and chose upgrade during install)
2. download the updates (securitybugs etc - e.g. see first page for information about SSH bug...). You can find the updates at the download places.
put all updates in the same dir on the server and run:
rpm -Uvh *.rpm
/sbin/e-smith/signal-event post-upgrade
/sbin/e-smith/signal-event reboot
That should be it...
Good luck
Greg