theres profession councilors, there should be one outside the starport in Eisley.
costs money, and it goes up each time you do it, might get a free one.
also, i think when going combat to trader, or trader to entertainer, or entertainer to combat etc you start back at level one.
exception i think should be changing within the same thing, combat to combat you would keep your levels, trader to trader should be the same, though im not sure if going combat to trader, then back to combat would keep your old co0mbat levels