A question i'm sure every 125 owner asks: how to i get more speed out of my machine?

I've got a lexmoto lsm125, not a bad bike by any means but the top end is a bit lacking. As far as i'm aware the best way to get more power is an aftermarket exhaust, bigger front sprocket (top end but lack of acceleration), new air box and a bigger jet for the carb.

I've got a new exhaust in the post so that's one ticked off the list. Now i'm not an idiot but not a genius when it comes to mechanics so i'm not too sure what i need to be looking for concerning the airbox and carb jet. Starting with the airbox how much of a difference does this make? Should i be looking for a bigger or smaller airbox? and what shape?
The bigger jet also stumps me a bit. what size should i be aiming for (bearing in mind the aftermarket can, airbox and sprocket i'll hopefully be fitting)? and is it difficult fitting a new jet?
Potentially i'd like to swap the flat piston for a crowned one, but i'm not sure if this would be worth the effort/money.

Obviously i'm not expecting a step by step guide but any help would be very appreciated! and before someone suggests i bore the thing out, i'm trying to do as many reversible upgrades as possible out of fear of any mistakes (not to mention the legality and voiding of my warranty).

Ta very much for any help!!!