How to determine kernel version - Which kernel are you using?

Find which kernel modules are installed

[root@plain chkrootkit-0.45]# rpm -qa | grep kernel
kernel-utils-2.4-8.37.7
kernel-smp-2.4.21-27.EL
kernel-pcmcia-cs-3.1.31-13
kernel-source-2.4.21-27.EL
kernel-2.4.21-27.EL
kernel-doc-2.4.21-27.EL

Find which kernel version you are currently running.

[root@plain chkrootkit-0.45]# uname -a
Linux plain.host.net 2.4.21-27.ELsmp #1 SMP Wed Dec 1 21:59:02 EST 2004 i686 i686 i386 GNU/Linux

From RedHat.com about upgrading kernel

To upgrade to a newer version of a Red Hat Linux kernel, you need to obtain the latest Red Hat Linux kernel in RPM format, install the new kernel from the RPM packages, and configure the boot loader to boot the new kernel.