Depends on your class, quest will be different. Take the quest "New Job" from Shilly and it will direct you to a class trainer to get the next quest. Once you have completed your job change quest you will get a skill reset potion.

don't remember exact name but I believe you first go to Shilly (npc) to start the job change quest (thats the skill reset 30 stuff) and then you end up going to specific class npc.

probably someone will post the exact name of the quest.