Except in the cases in this article mentioned no written will, nor any part thereof, can be revoked or altered otherwise than:
1. By a written will or other writing of the testator, declaring such revocation or alteration, and executed with the same formalities with which a will should be executed by such testator; or, 2. By being burnt, torn, canceled, obliterated or destroyed, with intent and for the purpose of revoking the same, by the testator himself, or by some person in his presence and by his direction.