What do you mean by "improve" your top end? The stock ratio is darned near perfect for true dual-sport riding. However, if you are a single-sport rider, or you must tinker, experiment with ratios by changing out the rear sprocket. It is easiest to change. Change your front only when needed because the current front is worn and needs changing anyway. It is a pain to take off the left case cover to change the front sprocket. Pre-purchase a gasket or 2 to have on hand for the job. Have an extra set of hands to help you re-install that left cover to help keep the stator wires where they should be so they don't get pinched or cut, which almost everyone has done because as carefully as you try to place it, the magnets make everything go wonky.