On my recent trip from Amsterdam to Boston to Iowa to Amsterdam, I needed to move my last set of flights forward a day because of an important meeting. I called up American Airlines, and because my Boston to Iowa trip had been delayed, AA didn't charge any money to change my flight to Amsterdam.
If you ever need to reschedule flights, AA will be very accommodating if you've had previous delays. This is probably true for other airlines. I hope someone finds this tip as useful as I did.