you could change the rear sprocket and add a couple of teeth to it. You would be surprised how just adding two teeth to the rear pep it up a little. this does not always mean more is better. I only do two teeth at the most, but that is just personal prefferance. you could change the front sprocket by dropping it down one tooth. this is the cheaper of the two. If you do change either one always check chain clearance, so that is isn't rubbing on anything. by no means will these changes make it run like a 250 motorcrosser but maybe it will keep you interested in it a little longer and this will help you hone your skills alittle more before stepping up to your next ride.
also keep in mind that when you change sprockets this also affects the length of the chain. meaning if you add too many in the rear your chain could be to short and will need to be replaced, or by dropping one tooth in the front if the chain is worn out it could end up being too long and will have to be shortened.