If you dont want to check the fare rules, then the only fully refundable tickets are the Fully Flexible fares which can be a lot more than the Flexible.

That said, most Flexible fares are fully refundable but with many junk fees associated with changing dates because it carries many embargo periods. However if travel not started and you want a change, the best approach is just cancel the ticket, get full refund, then buy what you now need.

I use a quick and dirty way to go thru the Fare Rules, which, AA makes it SO ANNOYING to find as it do not show up until the Last Screen and in tiny clickable bubble. All you need to look for $ and figures in the Refund section. If you dont see any, it is fairly certain there is no fee to cancel on fully unused ticket before travel.