8) Can I upgrade my flight seats just one-way?

TUI flights

Round Trip Bookings

For round trips, you can upgrade your seats to Seats with Extra Space, Extra Legroom Seats or Premium seats, if they're available, until three days before you're due to travel. You'll be able to do this by contacting us.
 
Outbound Flights
If you want to upgrade to Seats with Extra Space, Extra Legroom seats or Premium seats for just your outward flight, you'll be able to do from two days before the date of your outward flight or at check-in, if they're available. Alternatively, contact us for more details.  

Inbound Flights
If you want to upgrade to Seats with Extra Space, Extra Legroom seats or Premium seats for just your return flight, you can do this from nine days before your return flight up until 25 hours before, if they're available. You'll need to contact us to book these upgrades, or you can speak to your Holiday Rep while you're on holiday.

Flights with other airlines
If you're flying with one of the below airlines, then please follow the above guidance.

Air Europa (Flight prefix AEA)
Albastar (flight prefix JQ)
ASL Airlines France (flight prefix FPO)
ASL Airlines Ireland (flight prefix ABR)
Evelop Airlines (flight prefix EVE)
Germania (flight prefix ST)
Norwegian (flight prefix D8)
Travel Service (flight prefix QS)
TUI operated by Norwegian (flight prefix BY)
Volotea (flight prefix VOE)

For all other airlines you may be able to do this whilst you're checking in online if you've been given a separate flight booking reference.