Mandi, it depends on the rules of your ticket, if it is changeable with or without pen, then you can have it changed. for the excess amount, if it is non ref, most likely it becomes a credit for your next booking.

if its refundable, then it shall be credited back to your account.

i suggest call the airlines first and have the rules and restriction checked.

I think I've discovered the secret of life - you just hang around until you get used to it.  ~Charles Schulz