as far as upgrading a video card in a laptop there is really no point...first off its pretty much impossible and secondly if it was possible it would cost more than a new laptop lol...that being said what model laptop do you have and what screen saver are you trying to run (sounds like its a battery waster to me)
you can try updating your gpu drivers and see if that helps...is this the only issue you have that it cannot run the screen saver you want?
laptop gpu changes are only doable if you have a laptop that offers different gpus for that specific model. laptop gpus arent fit one fit all like desktops are. Most of the time, if your laptop was not customizable, then only the ram/hdd/cpu sometimes can be changed. the other method is by using a docking station but doing so is extremely expensive and not worth the cost.