from:
https://www.delta.com/content/www/en...tificates.html
REDEMPTIONS ON AIR FRANCE
Valid on most transatlantic flights operated by Air France.¹
One-way upgrade from Main Cabin when booked in Y, B, or M class to Premium Voyageur Class.
or
One-way upgrade from Premium Voyageur when booked in S or W class to Business Class.
¹ Not valid on AF operated 747 aircraft flights; only valid on flights with the Premium Economy Ca