Hey everyone! I'm taking my dad to ANTARCTICA in November for his 70th birthday! We're both hitting our seventh continent together so it will be a very special trip. I was hoping we could get an upgrade to Delta One but now I'm not sure that's a thing? Can someone please explain this to me, so I can manage my expectations? Also, if a free upgrade isn't possible, can I buy one the day before or day of cheaply? Delta One isn't even half full and there's like 38 of them!

I'm Platinum Medallion, we're flying from DTW-ATL-EZE on the way there - this is the plane: Boeing 767-400ER (764) Layout 2 (includes Premium Economy)

The way back we're flying LIM-ATL-DTW and the plane is a Boeing 767-300 with C+ and Delta One but no Premium Economy.