Originally Posted by
pitz
Just do on-line check-in early within the 24-hour window. Almost 100% guaranteed that you'll be able to swap to your seat of choice, since many seats go unassigned (in particular, the people who didn't pay for seat selection -- a seat is still allocated for them, but not assigned..and some of those seats are window/aisle).
I would agree with Pitz. Online check in allows you to change your seat depending on firm assignments. I twice was able to get to the front of the economy section, once on a UA metal into their United Plus section with it's slightly more space.
Best of luck.