Q : I have installed the desktop version 'KUbuntu 8.2.64-16 generic'. Now I want to upgrade this to Kubuntu server version. How to do?

A:All Ubuntu derivates (Ubuntu, Kubuntu, Xubuntu, Ubuntu Server,...) are the same distribution. You can install services like Apache or MySQL under every Ubuntu derivate.

but you can at least upgrade to the server kernel :

$ sudo apt-get update
$ sudo apt-get install linux-headers-server linux-image-server linux-server