See below for some short instructions on how to upgrade your existing XBMC Live installation to the latest SVN version. These instructions should also work for regular XBMC Linux users as well. It is particularly important to update your XBMC to the latest SVN version if you plan on using some of the latest and greatest plugins and skins. For example, after I installed the Aeon65 skin I noticed that the skin would crash when I would go to certain views... many of the people on the forums recommended upgrading to the latest XBMC build so I did exactly that...

Installing from the PPA builds can be risky, so it's highly recommended that you back up any critical information. If you accidentally break something during the ppa upgrade, keep in mind you can always re-install from one of the official builds. That being said, I recently upgraded to the Dharma Beta1 install in under 5 minutes with these commands:

Updated Instructions

Run the below commands via shell / terminal and your box should install the updates and reboot with the new version of XBMC installed.

sudo add-apt-repository ppa:team-xbmc-svn/ppa
sudo apt-get clean
sudo apt-get update
sudo apt-get install xbmc
sudo reboot

Original Instructions

These are the original instructions that used to be on this blog post. They use a more manual method of adding the PPA repositories which is confusing for some people. They also explicitly identify with the Ubuntu 'Jaunty' build and are generally just confusing for most people. I've left them here for the time being for reference purposes, but may archive them into another post in the future.

Add the repositories -- first open a nano editor for the third party sources list:

sudo nano /etc/apt/sources.list.d/xbmc.org.list

Then copy and paste the following respository entries:

deb http://ppa.launchpad.net/team-xbmc-svn/ppa/ubuntu jaunty main 
deb-src http://ppa.launchpad.net/team-xbmc-svn/ppa/ubuntu jaunty main

Import the key:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 64234534

Update your repository list

sudo apt-get update

Then do the recommended upgrades:

sudo apt-get upgrade

Now install the latest XBMC:

sudo apt-get install xbmc

And reboot your system:

sudo reboot

I should note that after the installation / upgrade, I started getting an error message about needing OpenGL rendering enabled. A simple reinstall of the NVIDIA drivers will get you back up and running. The first time I ran into this problem I was pulling my hair out trying to get it fixed -- just read this post and you'll be back up and running in no time.