Updating KDE 4.2 to KDE 4.3

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First open the list from a command console as follows:
sudo nano /etc/apt/sources.list

Add the following line at the end of the file:
deb http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu jaunty main

Add the security GPG keys as follows:
gpg --keyserver keyserver.ubuntu.com --recv 2836CB0A8AC93F7A
gpg --export --armor 2836CB0A8AC93F7A | sudo apt-key add -

Update the packages:
sudo apt-get update

Install the new updates:
sudo apt-get dist-upgrade

And reset the computer for the new KDE to take effect.