I am almost ready to redeem my USAir miles for an award.

But I am a little unsure about my return date. I wonder if I should redeem while the seat is available.

Does USAir charge $150 just for a change of travel date later? Or is the fee lower? Reading the terms and conditions I am not sure how much it would cost me to redeem now and change return date later (if necessary). If the change cost is $150 I will not redeem now. But if it is a small fee I would.

Thanks for your advice.