Grand Master Rains:
To become a Rogue, you need the appropriate level and token. Your level must be at least 20 to qualify to change profession. You also need a token to prove you have passed the Test of the Rogue, as well.
However, it seems that your level is not high enough, and you have not yet passed the test, either. First, try to raise your level to 20 or higher. To take the Test of the Rogue, look for Captain Bezique of the village of Gludin. Go straight to the west to get to the village of Gludin. Captain Bezique is at the western entrance. To become a Rogue, pass his test and bring back his recommendation.