Obtaining the Kernel Sources
Every Linux distribution contains kernel sources. Red Hat offers install options to include the kernel headers, and a separate RPM to include the kernel sources. You must install the kernel headers if you plan to compile any software; to build the kernel, you must also install the kernel-sources RPM, or obtain kernel sources from some other source.
When fetching kernel sources, it is good netiquette to seek a mirror site as close to you as possible. Although famous sites such as Red Hat (ftp://ftp.redhat.com) and kernel.org (ftp://ftp.kernel.org/pub/linux) will have the files you need, you should check http://www.kernel.org for an appropriate mirror site.
Before you replace your kernel sources, ...