its 4 stroke air cooled so its a very laid back engine its going to be either based off a CG or CB 125 engine, 4 stroke 125 engines are very rare to be deristricted i can only think of 6 and there either a minarelli WR125 engine or a Derbi DB125 engine and both of those are liquid cooled 4 valve engines that are just capped to meet learner restrictions.
you could jet up the carb so its a richer mix but then it'll run hotter more likerly to be unreliable from this, change the carb to a bigger one same pro and cons, a unrestricted CDI so it revvs higher but tehn you could blow it and the heat thing once again.
safest thing for more speed is sprockets but gearing it up has its downsides aswell taking longer to get to the top speed and loosing some low down torque and you'll really feel the reduced torque especially in head winds.
a 150cc bore kit could work for some more 00mph