From AA:
https://www.aa.com/i18n/aadvantage-program/miles/redeem/award-travel/upgrade-with-miles.jsp
Upgrade with miles
Enjoy a higher cabin of service
Use your AAdvantage® miles to upgrade on flights marketed and operated by American Airlines or American Eagle for yourself or anyone you designate.
Upgrades are valid to the next cabin of service and are valid for a single one-way trip with a maximum of three segments. Upgrades are subject to capacity controls. Excluding award tickets and Basic Economy fare tickets, the following eligible fare types can be upgraded:
Discount Economy with published fares booked in H,K,M,L,V,G,Q,N,O,S and Military or Government fares booked in Y
Full-Fare Economy with published fares booked in Y
Discount Premium Economy with published fares booked in P
Full-Fare Premium Economy with published fares booked in W
Discount Business with published fares booked in I
Full-Fare Business with published fares booked in J, D or R