Delta has a bad habit of making program changes without giving any announcements to SkyMiles members. Earlier this month, Delta tweaked their award chart and the changes were never published. Airlines usually tend to inform about the changes to their award charts few months before to let program members time to issue awards at old levels.
Now, Delta has quietly withdrawn the ability to use miles and upgrade instruments for upgrades on KLM on M-fares. You can still use them on Y and B fares. You were previously able to upgrade using miles or upgrade instruments from all of these three. There has been a change to Air France upgrades as well. You can still upgrade from YBM fares to premium economy, but the ability to upgrade from premium economy to actual business class has been discontinued.
Delta’s website still happily lists the fare classes that are no longer eligible for upgrades as of today (September 27).
Delta should really step up to the plate and have a proper communication about the changes to their SkyMiles program. Their website still lists wrong and outdated information about the fare classes that one can upgrade using Delta miles and upgrade certificates on KLM and Air France flights. There are simply no excuses for this.