Please take my advice - keep riding your 250 for at least another year. Your choice of a Kawa 750 is a good choice. There is absolutely nothing wrong with that bike but consider this. It's 3 times more powerful, heavier and bcs of its power, it will make you want to overtake everything in front of you. Riding a 250 means you havent got that experience yet.
You say you are 16...a great age to start your appreciation of bikes. I would keep riding your 250, study the 750 over the net, learn about the engine, the braking and if you are a serious biker - fork out a little money to get some professional pointers and training. If you do, not only will you look good on that machine, but you'll be able to handle it like a master.
Ride safely, respect yourself and your bike.