I would just do the top 1/3 as pookiebear said. When you do it shave it into a V shape. We just used regular clippers we had from Walmart, Wahl brand. Make sure you have you fingers on the opposite side of the ear though when your shaving so the ear is flat to avoid nicking. I have heard that some Yorkies ears do not go back up after teething but most do. You can never tell, every baby is different
Good luck