Stock gearing is 39 rear, 16 front.
Changing to a larger rear
sprocket, or a smaller front sprocket will make the bike quicker therefore making it feel like it has more torque.
easier and cheaper solution is to change the front sprocket (counter sprocket ). 1 tooth less on the front sprocket is roughly
equal to 3 more on the rear. Putting a smaller sprocket on front is quicker since it only has a circlip holding it on. And
you won't need a longer chain, which might be needed if the rear sprocket is too big. They cost less than rear sprockets too,
roughly $12 for front and 3x that for rears, give or take. Change stock front to a 15t. for quicker accelerations but you
will lose some top end and the bike will rev higher at a given speed (most noticable at highway speeds). Too small on
the front sprocket though and your chain will bind up-bad, very bad.
This will not affect your speedo reading but will affect the engine RPM at a given speed; drop a tooth front or rear
and your engine speed will increase for a given speed, so you'll lose a little top end as a result.
This will affect your gas mileage.