Sand paper and lots of elbow grease then get some polishing rouges and but a buffing wheel for your electric drill and go at them with the rouge and buffing wheel. My advice, don't do it, way to much work, but if you want to there you go. Just start out with a courser grit sandpaper then gradually work to 220 them use the rouges. Go from the coursest to the smoothest and buff it untill it shines like you want them too. Afterwards I recomend clear coating them for ease of cleaning and upkeep.
HK