How many miles to upgrade?

My wife and I just bought our tickets to fly from Pittsburgh to Tokyo via Detroit in October in comfort. I'm 6' tall and was not going to do a 13 hour flight in regular economy. Since we are already in comfort I was wondering if anyone might know how many miles it would take to upgrade to premium select for two people on one leg between Detroit and Haneda I see 0 need to upgrade between Pittsburgh and Detroit since we will be in the air less than it would take for me to go through security and get to the gate.