You can change jobs to a Thief in the Desert City of Morroc. If you apply at the Thief Guild - located in the center of the 1st floor of the Pyramid, 10 o'clock direction in town - you will be given a task. The Thief job change task is to gather mushrooms from a Mushroom Farm full of Monsters. It's a test to evaluate agility and judgement. Orange Net Mushrooms are 3 points each, and Orange Gooey Mushrooms are 1 point each, and you will be evaluated at the Thief Guild once you have enough that add up to 25 points. Requirements are Job Lv 10.