If you are running CentOS and want to update all the software that was installed via yum. You can execute the following command, yum will download the updates and proceed to install them.
You should be the root user to be able to execute the commands below. After the update process has been completed you should exit from being a root user and run any further commands as a regular user. This will help to prevent any accidental damage from being done as a root user.
yum update