Quantum GIS is an opensource software which is rapidly growing among community. Hence, you may be need to upgrade it to the very new version (stable or non-stable). To get all new features work, you have to uninstall the old QGIS before install the new one.
1. Fetch new version from Ubuntu’s repository
sudo apt-get update
Remove the old QGIS
sudo apt-get autoremove --purge qgis
Install the new one
sudo apt-get install qgis python-qgis
Caxradonya 