Originally Posted by
m3red
Remember you would need to buy a flex ticket to gurantee you can upgrade before check in.
Buying a flex fare guarantees that you ticket will not have the 24 hours upgrade restriction. However, some saver fares also don't have this restrictions as well. X, V, T, L, Q, H are only the saver fare classes that can't be upgraded until 24 hours before check-in.