Apart from phoning up AAdvantage and spending ages on the phone and driving the AAgent crazy, you will have to credit at least 3000 miles in the Jet Privilege program to make dummy bookings.
What route and dates are you looking to change to? maybe we can help you out?
BTW, they will always release 1 seat on each flight and you got zero chance if your using NON-JP miles for booking a second seat.