Following the instructions at:
https://launchpad.net/~anders-kaseorg/+archive/subversion-1.6
Edit the apt sources, using your favorite editor:
$ sudo emacs /etc/apt/sources.list
Add these lines to the end of the file:
deb http://ppa.launchpad.net/anders-kaseorg/subversion-1.6/ubuntu jaunty main
deb-src http://ppa.launchpad.net/anders-kaseorg/subversion-1.6/ubuntu jaunty main
The add the key signature:
$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 413576CB
where 413576CB is the Signing Key from the web page above… update the apt cache, and force a reinstall:
$ sudo apt-get update
$ sudo apt-get --reinstall install subversion