It doesn't hurt to just remove the old card, and insert the new. Most likely it will work if the driver is the same.
At the worst, you can do the delete driver and cleanup the registry bit.
If you change nvidia/ati, then it is best to uninstall the old card, delete the old software, and install the new card.
It will operate in basic mode without a driver. Something like 640 x 320 resolution. Enough to navigate the internet and download the proper driver.
If I planned ahead, I would have already downloaded the new software.
Personally, I always go to the graphics web site to get the latest driver, and not use the cd.
In the past, when a new generation of cards was launched, the cd was a better option. Probably specific testing for that card.