Final answer:
Once the flight has taken off, it is typically not possible to switch seats as passengers are required to remain in their assigned seats for safety and security reasons.
Step-by-step explanation:
In this scenario, the passenger is requesting an upgraded seat on Flight #339 which is already in the air. However, the upgraded seats are located in aisles 1-5. Once the flight has taken off, it is typically not possible to switch seats as passengers are required to remain in their assigned seats for safety and security reasons. The passenger would need to consult with a flight attendant or airline staff when the plane lands and inquire about the possibility of changing seats.