Apologies, I suspect this is a silly question, but I still haven't got my head around the NW-DL merger very well.

I'm wanting to fly MAN-CRW on an M fare to upgrade to BE. As per the usual upward trend with M fares, the more direct MAN-ATL-CRW prices out at £1600. But, if I go MAN-AMS-DTW-CRW on the way there, it comes down to a more civilised £1200.

AMS-DTW is on NW243. Can I upgrade that using my DL miles? If so, what fare bucket I am looking for within J? Having checked expertflyer, it seems unable to even find NW243 on the day I want to fly (25th Nov.)

Thanks.