You un-install the old software from your hard drive, but it’s still running in the background.
After shutting down, swapping out the card, and starting again, your computer will sense the new hardware, and ask you to install the drivers.
This may seem obvious, but to some not familiar with PCs, it isn’t always the case…keep in mind the software being uninstalled is only that related to your graphics card drivers and diplay management software, nothing more. For nVidia, I believe their nVidia drivers uninstaller removes all software applicable; for ATI, I’m not sure…you might have separate uninstallers for Catalyst and/or Hydravision.
If upon uninstallation and reboot you have any problem at all, rebooting again and holding down the F8 key after device detection is complete should cause a more detailed boot options menu to appear, from which you can choose a VGA boot mode that uses a very basic display driver. I’ve never had to do that myself.
Following on from what John said, some manufacturers may vary in how they want you to install the drivers. Namely, even if your card is detected and you are prompted to insert the installation disk, some installers will instruct you to cancel that prompt and run the installer directly, after Windows has completely initialized. Just review your installation instructions and follow them, and you should be fine.
Regards,
Daryl
