Since you're using Red Hat, the easiest way to upgrade your system is to use the up2date utiltiy, First you need to register by running the following commands:
1. rhn_register --config #to configure the rhn_register put a proxy
2. rhn_register #to register to RHN
3. up2date --config #configure the up2date utility put a proxy
4. up2date #will automatically download and update your system
Or you may just download it manually from this site:
http://www.redhat.com/errata
