I'm surprised to hear this question coming from you -- I would imagine it's a fairly simple task?
I would try finding the four-finger swipe-up or swipe-down in the default configuration and edit the action associated with the gesture, just pick the opposite direction for each gesture. I'm sure you already tried that though?
I haven't got the FW software installed (damn you, Windows 7) so I can't confirm my assumption. But I hope it will work!
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