go to the retainer vocate in any city, one of the options tells you what jobs each class turns into. If you already gave them a job stone you cannot change it without starting from lvl 1, if they are still a class though all you need is a "modern vocation" which is from the same guy who tells you the class to job

sam and rdm you need to take a class to 50 just because there are no weapons under lvl 50 for them