I booked the upfront seating primarily because I wanted the large bag and to be able to choose seats.
Unfortunately the only available seat left in the "upfront" area is a middle seat. I thought that I'd be able to then choose a standard window seat since I paid for a seat assignment.

Am I permitted to change to any standard seat? I'd prefer a window seat. If I try to select it, it seems like my "Large bag" goes away.
Is this correct? If I pay for "upfront", I must sit in the "upfront" area or lose my "large bag"?