Originally Posted by
Diabeetus
You can pay for them at the time of purchase. If you have already bought a ticket, then you can use the "manage my bookings" link on the website, and move into one of the "preferred seats". Either way, there is a charge associated with it.
I just noticed the "preview seat availability" link next to the flight I select early in the booking process. That was the missing element; now I can see if there is a preferred seat in the exit row before purchasing the ticket.