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

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 3 days before you're due to travel. You'll be able to do this by using Manage My Booking or by contacting us.

To check if you've got access to Manage my Booking, take a look at our "What is Manage my Booking?" question. 
 
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 2 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 9 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
You'll be able to do this whilst you're checking in online if you've been given a separate flight booking reference.