I might as well add this note before the thread disappears from the front page:

As it turns out, all it takes for a run-of-the-mill adventurer to change classes is some studying (and perhaps a senior adventurer to sponsor his education).
So, there. There's nothing particularly unique about changing classes. It's no different from choosing a new career, and learning all about it as you go along. It just happens that the WoL (and possibly those with the Echo) learns faster than the average Joe.