I would say just change one or the other. The front one is much easier to replace. If you replace the front one go 1 tooth smaller. If you replace the rear sprocket go 1 tooth bigger. It will gear it a little lower make a little more torque.
I would also Suggest Starting in 2nd gear too if you're racing.
Hello Honda family I need your help I got a 2007 trx 450r I put a new plug in it rode it down a half mile just to warm it up got ready to turn around an it shut off on me all it do is spins over it’s getting fire I changed the plug it’s still not doing anything