If you want to update your kernel with rpm then you have to follow the following steps :
1. log-in to your Linux Server with your root access.
2. Run the following command to find out recent kernel availability on your server.
3. You have to edit grub.conf to new kernel availability.
4. Run the following command to download latest kernel version from kernel.org
rpm -ihv kernel-smp-2.4.21-47.0.1.EL.i686.rpm
5. You have to make new kernel as a default kernel
0 in /boot/grub/grub.conf
6. Reboot your server with the following command.
#shutdown -r now