Hi. I think an easy way to update it would be using synaptic (you probably have a ksynaptic program, or whatever you use to install packages), and selecting the "mark all upgrades" option.
I've heard ubuntu upgrades very safely, but if you use another distro, and lose you x server, your kdm or something (you have only the terminal available), you will still (probably) have "aptitude". By which seaching maybe only for "kdm" (?) you should get your GUI back again.