Be sure you understand the fare premium you'll need to pay above lowest published fare in order to be eligible to upgrade on Delta, KLM, or AF metal.
For all other International markets, Mileage Upgrade Awards on Delta-marketed and operated flights may be used to upgrade on published Main Cabin fares booked in Y, B, M, S, H, Q, or K class.
For flights marketed and/or operated by Air France/KLM, Mileage Upgrade Awards may be used for a one-class upgrade on published fares booked in Y, B, or M class.
http://www.delta.com/content/www/en_...de-awards.html