Change gravity in game???

Hi
I want to create a game where the player presses something that changes the gravity in the world so that the player would go up. Is this possible? If so how would I do it and if not how could I do it?

I am brand new to Unity and have only messed around with it a little but want to create a full game and this was my idea. Thanks in advance.

You can change the gravity from script like so: Unity - Scripting API: Physics.gravity