I have Ubuntu 12.04 installed on my laptop and I want to remove it and install Ubuntu Server. How would I do that?
Download the server install CD from here Ubuntu 12.04 - Server Install CD burn it to a CD , boot from CD and re-install.
See here a tutorial about sever installation : Ubuntugeek.com and better would be to install first in VirtualBox to see how the installation progress is and then make it for real.
About VirtualBox see here: Ubuntu community wiki- Virtualbox