Well it depends a bit on the hair style. If the hair has a skullcap you need to select that if it doesn't you just select the hair style itself.
You then go to the posing tab and generally adjust the scale. Some hairstyles also allow you to adjust the Z-axes (height) which might solve it.
I'm guessing that you can also use mesh grabber if you have that addon to adjust the hairstyle a little but I don't think I have tried that myself up until now.