Considering you purchased an upgradable ticket, chances are your change fee is nominal (multiplied by 3). There won't be much fare difference to pay. I would keep checking in frequently for a more direct routing and pay the administrative fees.

Also, do consider a stopover in the west coast both directions. I once travelled with my 5 month old nephew and wouldn't subject everybody around me to a screaming tot on a DTW-NRT flight (or MSP-NRT for that matter). It's a more civilized way to travel leisurely.