Grand Master Pabris:
To become a Warrior, you need the appropriate level and token. Your level must be at least 20 to qualify to change profession. You need the medallion of the Warrior to prove that you passed the Test of the Warrior, as well.
However, it seems that your level is not high enough, and you have not passed the Test of the Warrior, either. First, try to raise your level to 20 or higher. If you want to ask about the test, seek Master Auron in the village of Gludin.