First id get a stroker, cam, CDI, edelbrock carb, P&P, and good exhaust and intake set-up. Then id go for Wicked +2 or +3 a-arms, and a good set of Elka's. That should be most of your money. Buying a new quad is pointless, a raptor660 suspension isn't going to be as good as the warriors with all those upgrades, and banshee suspension is only slightly better than the warriors stock, and a yfz is going to cost more than 4000 for one thats in good shape.
And another thing, someone gave you the quad, and I'm assuming that would be your parents, i don't know about you but if my parents just gave me a quad id be happy with it all stock. Also don't you think buying a whole different quad would be kinda harsh toward them, i know if i were a parent and my kid just totally disregarded the quad i paid for with my hard earned money id feel pretty bad.