1) open hplip (from the tray)
2) uninstall the printer
3) run hp-setup as root to install the printer again (from a terminal run sudo hp-setup )
For more information :
# How to Uninstall HPLIP
http://hplipopensource.com/node/188
# Manual Build and Install Instructions for Ubuntu
http://hplipopensource.com/hplip-web/install/manual/distros/ubuntu.html
