Hmm.. im not sure where to get the redhat kernel for enterprise as I don't use it. However, if you can locatate it, get the regular kernel ( not the SMP or BIGMEM Kernel ) and to install:
rpm -ivh filename.rpm
A quick lazy way to check what boot loader you are using:
If one of those returns an error ( file not found, etc ) then chances are you are not using that bootloader.
If you are using lilo, then after the rpm install above, "pico -w /etc/lilo.conf" and make the necessary changes. After that issue "lilo -v -v" and look for errors then "shutdown -rf now".
If you are unsure of what needs to be changed, then do a search on this forum and on google for help. Messing with the kernel, especially if you don't know what you are doing, could render your server useless. I would suggest getting a local test box and fool around with that or hire someone capable of doing the work for you.