Adobe Illustrator: How to make window smaller?

I've created a vector image to be exported as an png for an iphone match 3 game. When preparing to export, the preview shows my graphic is in the bottom right hand corner of a large grey window. When looking at it while editing there are scrolling bars on the bottom and right sides of the the window. I think the window is too big; too much grey space. How do I adjust the window size to perfectly frame my image?