The TT250 muffler is hollow with packing and no spark arrestor. At the "back" of the muffler, you will find a cat converter that looks strikingly similar to those round corrugated cardboard cat cons you see for sale in the Wish ads on Facebook. Behind that is a baffle.
The majority of the restriction in the factory exhaust is going to be at the end cap to the muffler can.
Remove the 3 hex head screws and remove the end cap. Use a hacksaw and cut off the "nipple" at the end of the exhaust can as close to the can as possible. Then take a 1 1/2 inch metal hole saw and center it on the exhaust hole in the can. Cut your hole. Reinstall the end cap and the three hex head bolts. Use some sort of Loctite on the threads or they will rattle loose. This will maintain your clean, factory look.
I would recommend leaving the cat and baffle behind it in place. The increase in sound and flow will be significant enough. For more sound and flow, remove the snorkel on the airbox. Its only glued in place, and can be easily returned using silicone if you ever decide to do so.
You will absolutely need to rejet and retune your carburetor after doing this. Order a jet kit before you begin.
Don't do any of these things until the bike is completely broken in and out of warranty. In fact, don't do them at all.
