Most cash bookings can be upgraded with Avios either at the time of booking or later on, depending on availability. Only the lowest economy (World Traveller) fares (Q, O and G) cannot be upgraded with Avios at any time. There must be reward flight availability in the next cabin for you to be able to upgrade to it using Avios. You won’t be able to upgrade with Avios at the airport or on board.
First class service was formerly available on intra-European flights on airlines such as British Airways, Lufthansa and Swissair. First class seats were typically configured in a 4-abreast configuration, similar to current North American domestic first class seats, rather than the 6-abreast configuration used for economy and latterly business class services.