While cancelling and rebooking is the only "self-service" option, I prefer to call in and ask for a re-fare. This method preserves your PNR #, seat selection, and meal selection if made. (Assuming the agent does it correctly.) If you did the cancel and rebook yourself, you'd need to put the second PNR on hold, cancel the first and await the email with your credit voucher/ticket number to apply to the new PNR, and then you'd get a new credit for the difference emailed to you when then second is ticketed. You'd also have to reselect your seats in the second PNR as you already are sitting in them in the first PNR. If you cancel the first before at least holding the second, you risk the possibility that your new fare will not be available when you reticket, although that is not too likely if the fare has dropped.

As far as the connection time just be aware with AA if you misconnect (especially with two of you), the chances of getting the front cabin on the next flight will be very low. And the compensation AA will offer for the downgrade is generally considered woefully low by those receiving it.