I recently treated myself on a haul from JFK to London using miles. Since AA overhauled their system, the best way to do this is via "Instant Upgrades." I just logged into the app, opened my trip, and a pop-up offered Business Class for 25k miles + a co-pay. It’s way smoother than the old waitlist days where you’d pray at the gate. Just keep an eye on your reservation daily, as the "mileage price" fluctuates like crazy. I grabbed mine three days before flying when the price finally dipped!