i'm not 100% sure, but you could probably fit one or MAYBE two inch bigger diameter rim than the stock. The stock one has 16's correct? then i would not go any bigger than 18's, one: it might not fit very well or at all and two: i hate the look of ginormous rims...
i'd probably go with some 17's, best look of an agressive rim size and it should fit nicely, with some lowER profile tires.