I wouldnt bother upgrading it mate, just sell it and get a PitBike 110cc or just get a CR,KTM,YZ,RM,KX 125/250 so much fun :D.
MrRob i assume u've never had one ? They are fun i loved my MidiMoto untill i came off :D, then i sold it for a PitBike 110cc untill i sold that for a sccoter lool...