You can try resetting the cycle, but you probably have to replace the window regulator. That's the switch that feels the door handle pull and tells the window to slide down a little.
To reset the window's cycle (resets the height too if anybody has wind noise due to a gap), remove the battery's negative terminal for a few minutes. Make sure you have your radio code before you do this or the stereo will be useless until you can get to a dealer and get the code. Replace the negative battery terminal then put the key in the ignition and turn it to on, but don't start the car. Roll the window all the way down then all the way up. After it's all the way up, release the window switch then hit the up switch again. That records where the window stopped. Do both windows within 60 seconds of turning the key to on. Next, turn the key off and leave it for at least 10 seconds, then you're ready to go.
Part number for the regulator is:
Right (passenger): 99654207604
Left (driver): 99654207504
List price is $175.66 so you probably want to go to Sunset Porsche for the part.