u/some-random-thought

Hi,
I have scheduled Delhi LHR economy seats booked for parents and me for June end.
Trying to understand what could be the upgrade option strategy and generally how much it may cost for premium economy and will it be worth it? The plane is generally B787-9 Dreamliner though it used to fly A350 too.
I am not seeing any option on the website as of now to upgrade seats.