Grand Master Helminter:
Regardless of your occupation, you must reach at least level 20 before you can obtain the right to transfer to another class. Likewise, in order to become a Dark Wizard, you must be at least level 20 or higher, and you must also possess proof showing that you passed the test of a Dark Wizard.
I am afraid that you are unqualified for several reasons. First of all, you must devote all of your efforts in attaining level 20. Then, you must undertake the test of a Dark Wizard and obtain proof called Jewel of Darkness and bring it back to me. You can take the test of a Dark Wizard from Witch Varika, who lives in the Dark Forest. You will find her praying at the Altar of Rites in the southern part of the Dark Forest.