Change flights - Get screwed
 

What US Airways fails to advertise when you cancel a trip is that:
1. If you buy a ticket of lower value, you lose the difference.
2. They will charge you a rebooking fee of $100+.
3. They will not take the rebooking fee out of the difference.
4. They will force you to rebook by phone and charge you $25.

Note that US Airways is so disorganized that if you call multiple times, you will get different answers. So call until you get the answer you want.