LCA sells airport upgrades, providing there are seats/crew/meals available.

They do not push the CE cabin beyond row 15, so cannot therefore sell more than 74 CE seats/upgrades.

If it's cabin crew of 7, instead of 8, they are further restricted on the maximum number in CE.

There would need to be meals available.

With the above 3 caveats, you should be able to upgrade on the day at the airport. The price used to be EUR150 if I am not mistaken.

The POUG price is EUR99, so it may have come down to match, I'm not sure. Keep checking though for POUGs, which may appear if I class inventory reappears for your flight.