You can change jobs to a Merchant in the Port City of Alberta. Talk to the guildsman in the Merchant Guild, located in the 7 o'clock direction of the town. The test consists of delivering an item, just like any other Merchant would do. In the room next to the guildsman, deliver the box you get to the specified city and person. Once you successfully deliver the box, you will receive a receipt. The test is completed and you will be turned into a Merchant once you return the receipt to the Merchant Guild. Requirements are Job Lv 10.