CentOS ships with an application called yum that serves as our recommended tool for performing updates and package installation. Please see PackageManagement, PackageManagement/Yum, and this guide for Managing software with Yum.
A version of up2date is also provided that does not connect to the upstream vendor, but instead connects to the CentOS Network (CN) for updates. Starting with CentOS 4, yum will import the key, but only after the user sees the key and can verify it is authentic.
There is a separate FAQ question concerning how to import the CentOS RPM signature key.
Note on using yum: Starting with CentOS-4 we use a newer version of yum (as compared to CentOS-3), so there is a new metadata system that has the hdr files compressed in a single file (and not lots of small header files).
