Just uninstall old drivers reboot and install the new ones. If you want to be more thorough search around for tutorials on it depending on what company your upgrading from. Only need to go the extra step, like getting cleaners for the old drivers and registry when your going from ati to nvida or vice versa. Going from ati to ati or nvidia to nvidia poses no significant problems.
Also if you search around theres an internet spell checker useful for posting on forums and stuff. I want to use it but I haven't found it yet. Saw it on the screensavers once but didn't have access to the internet.