How to upgrade CentOS

Question: How do I upgrade my CentOS installation to a higher version?

Answer: Using YUM you can upgrade CentOS with only a few steps.

1. Backup your important data. If most or all of is in a database, make sure to backup all databases.

2. List all of the updates:

# yum list updates

3. Upgrade your distribution:

# yum update

4. Reboot the server:

# reboot

5. Verify that all systems are working:

# uname -a
# netstat -tulpn
# tail -f /var/log/messages
# tail -f /path/to/log/file
# cat /etc/redhat-release

Note: Because the kernel will be upgraded, you will need to reboot the server after completion, so you should plan a scheduled down time when your website(s) will have the least amount of activity.

Source: nixCraft