If you choose to change your seat you will be shown a seating plan. The 'person' on the plan indicates where you are currently seated. The blue seats are vacant, and by touching one of these you will be moved to that seat. For seat availability in other sections of the cabin, touch the cabin overview bar on the right of the screen or use the arrows to move row by row.
 The overview display to the right shows at a glance seat availability for the cabin. Touch this to move to other areas of the cabin to allow seat changes in these areas.