You need to have the PMUs in hand, and give the number to the DL CSA at the time of booking. (SWUs don't start until sometime next year, but they will be pretty much the same thing with a different name). DL will not book an upgrade unless you either have a PMU or enough miles in your possession.

You must book the ticket with a Delta CSA, not a NWA CSA. There must be U inventory available on the NWA flight (I had to go through DTW on my trip to BKK this summer on an M fare using a PMU).

Look to go through DTW and use NW341/NW340 when you have either the miles or PMUs. Depending on your dates, there should be some availability.