How do I apply package updates from the RHN or CentOS repo on CentOS / RHEL / Fedora / Red Hat Enterprise Linux?
You need to use yum command. yum is an interactive, rpm based, package manager. It can automatically perform system updates, including dependency analysis and obsolete processing based on “repository” metadata. It can also perform installation of new packages, removal of old packages and perform queries on the installed and/or available packages among many other commands.
The check-update option tells you if your machine had any updates that needed to be applied without running it interactively:
# yum check-update
Apply update to the operating system
Use the following command to update the operating system:
# yum update
Update a specific package
To update a specific package, such as httpd, use the following command:
# yum update httpd
To find more information about the command line options available for yum command, use the following command:
# man yum