hey bumblebee,
as the previous post states a bit more info including where you gonna kite average winds etc, really the best people to answer these questions is your instructor, then get the opinion of other kiters but remember every ones kite is best, the best way to get the right answers is to ask the right questions, like what dont you like about your kite, why did you choose to buy that one and not (poiinting at his mates kite) that one, how many kites do you own, why etc, etc, why is yours pink and his racing green, does that make it better? anyway you get my point, to get you started tallking averages, your wight in 15kn -18kn you would want nothing bigger than a 10, maybe a nine, once again depending on the kite, look at getting a slightly bigger board for learning with, 140 maybe then when you can kite get a smaller one and keep the bigger one for light wind days.
Hope this helps and have heaps of fun, your gonna love it!!!!!