Hello lilmini04
You can’t upgrade Supersaver tickets at all.
You would have to purchase a regular full fare point-to-point ticket (no saver offers) for 1st class in order to claim a refund.
I would simply travel 2nd class, the train won’t be that busy.
However, I rather see another issue with your ticket: we do not recommend using Supersaver tickets when arriving by air. If the flight is late, and consequently you can’t meet the train’s departure time, your ticket is lost. There is no alternative travel possible on the next train.
Kind regards,
Roland