If what i read is correct, that bike is not artificially restricted.. and if you don't want to spend money, you're gonna have to do it the hard way. The hard way is to modify things within the limits of the stock carb, engine and exhaust.
Carburetors can be bored out. The entire intake passage must be modified accordingly. The cylinder ports may be enlarged to some degree in certain directions... and in addition maybe some other serious cutting will help things.
Effective exhaust mods are tough if you have a stock muffler system.. There's not a lot you can do if exhaust is restricted, and those other modifications that help the engine breathe better might even be totally wasted when they hit the exhaust bottleneck..
so it kinda comes down to how much do you know about 2-strokes, about porting.. and what sorts of machines and tools are available and what kind of mechanical skills do you have.