4 strokes don't function that way
So different exhaust pipes don't have the effect they do on 2 strokes (big effect).
and ... you are also gonna find that 4 stroke mods are a lot more expensive than 2 stroke mods.
(and less effective)
you would need different camshafts and big bore kits and loud exhaust pipes.
And installing them is a LOT more difficult.
Truthfully .. you are better off just living with Hondas excellent engineering .. and enjoying what you've got.
Good acceleration and over 40mph top speed for a 50cc 4 stroke is pretty darn good.