AA's rebooking is right on its website and well worth reading.

No reason to cancel until just before the flight. If your flight is substantially changed or cancelled, you are due a refund. These days, it happens all the time and thus you have your money back entirely. If it does not, you can cancel for a credit and you are no worse off for having waited.

No reason to rebook until you are ready. In fact, as you must pay any fare difference and receive a credit for future tickets, this can become a costly effort unless you fly a good deal.