ML2T nailed it, I just want to add couple more things.
Mileage/VIP** upgrade allows up to 3 segments one way.
What you need to do is look for C inventory. AA will have at least 4 C seats available the day it puts the flight in the schedule, so the earlier you make your res and claim your upgrade, the better your chances to confirm your J seats and pick the best seats .
If there is no C inventory available at the time of your request, it does not mean you won't be upgraded, but you will have to play the waiting game till AA decides to open more seats, which could but doesn't have to happen.