Upgrades using SWUs on International Flights:
SWU's require RP or OP availability for upgrades on Delta operated flights and O availability on AF/KL flights. SWU upgrades can occur in advance or at the gate.

Delta - using SWU's requires a Y, B, or M (YBM) fare.

Air France - One-way upgrade from Premium Voyageur when booked in S or W class to Business class. Valid for booking on and after June 01, 2011. This cannot be done on flights operated by the 747, which does not have a PV cabin.

For a detailed description of this process - LINK.

Current discussion on if this program is going away:
http://www.flyertalk.com/forum/delta...premium-w.html

KLM - One-way upgrade from published Economy fares in Y, B, M, or U class for "KL" coded flight operated by KLM (flight number starts with KL) or in Y, B, M class for "DL" coded flight operated by KLM (flight number starts with DL) to Business class.

AF/KL Thread: http://www.flyertalk.com/forum/delta...rance-klm.html
Delta.com: Systemwide Upgrade Certificates

flyertalk thread on using SWU's on AZ: http://www.flyertalk.com/forum/delta...z-flights.html

Mileage Upgrades:
Delta Upgrade Awards

Upgrades on SkyTeam Partners:
Upgrades on SkyTeam partners require full Y fares, require contacting Delta to request/process, and can only be with full Y class fares.

Related flyertalk thread:
http://www.flyertalk.com/forum/delta...m-partner.html

Operational Upgrades (OpUp):
OpUps are when passengers booked in Y are upgraded to F/J because Y is oversold.
http://www.flyertalk.com/forum/delta...ve-thread.html
http://www.flyertalk.com/forum/delta...up-vs-swu.html

Related Threads:
http://www.flyertalk.com/forum/delta...nt-thread.html
http://www.flyertalk.com/forum/delta...er-thread.html