Grand Magister Devon:
To become a Shillien Oracle, the appropriate level and token are required. Your level must be at least 20 to qualify to change profession. Also, a token that proves that you passed the Test of the Shillien Oracle is required.
I am satisfied with your level, but it seems that you have not passed the Test of the Shillien Oracle. To take the test, you should find Sorceress Sidra in the Dark Elven Guild of the town of Gludio. You can change profession to Shillien Oracle only if you pass her test and bring back the orb of abyss as a token. You can get to the town of Gludio by following the road towards the east.