1. This has nothing to do with Flying Blue.

2. Have I understood you correctly that you are talking about an AF operated and coded flight?

3. If yes, the only thing you can do is upgrade with your Delta miles via the Skyteam upgrade scheme. This is from Delta's website:

Delta Mileage Upgrade Awards

You can use your miles for a one-class upgrade on most Delta operated flights. Mileage upgrade awards do not apply on all fares. To view the miles needed, see Delta Upgrade Awards.

SkyMiles members can also use miles to upgrade to Business class when flying on a full fare economy class (Y) ticket on many of our SkyTeam member airlines. In addition, as a result of our enhanced relationship with KLM, SkyTeam mileage upgrades can now be used on the following KLM booking classes: S, X, Y, B, and M. You will need to contact a Delta reservations agent by phone for more details and to process this upgrade request.

So you should not have any problems if your ticket has booking class Y (provided there is availability). Maybe slightly lower fare classes (I am thinking of B and K) are allowed, too; but for finding this out you would have to call them or ask in the FT forum for Delta Skymiles.