One of the tricky things with any Operating System is
upgrading the kernel of the system. Unlike the rest of the Red Hat
Linux, you can't just use rpm -Uvh, reboot the system, and
expect the machine to work any more.
The kernel is a special case. It can test your patience, but with the proper instructions you should be able to handle it. Just remember to stay calm, collected, and always to have a boot disk ready.
By following this guide, you should be able to upgrade your Red Hat Linux 4.2 and higher system to the latest kernel RPMs on the errata. I will go over what you will need to download, what you will need to write down, and go step by step through the upgrade and post-upgrade steps to get your system working.
Note: If you have compiled your own kernel from sources, these instructions can be followed, but you may need to tweak a thing here or there. In this case, my advice is write down what you have changed from the defaults, and make sure you have a working rescue boot floppy in case a problem occurs. [Both of these suggestions are good ones no matter what you are doing.]
This guide was written specifically for the Intel platform. I am using a Red Hat Linux 5.2 system as an example. If you are trying to upgrade to the 2.2.x kernels on a Red Hat Linux 4.x or 5.x machine, please see Updating to the 2.2 Kernel. If you have an Alpha or SPARC, you should read the sections that are specific for those platforms.