KDE team just released the 4.6 version of the famous Desktop Enviroment. Here it is a guide on how to install it on Kubuntu.
First you need to enable the Kubuntu’s backports repository, open a terminal and run:
sudo add-apt-repository ppa:kubuntu-ppa/backports
Once you have done that, to download and install KDE 4.6 run:
sudo apt-get update && sudo apt-get upgrade && sudo apt-get dist-upgrade