Subject to sections 8B, 16A, 20 and 20A, a will or part of a will is not revoked except—
(a) if the testator is a person to whom section 16 applies—by the testator expressing his or her intention to revoke the will or part of the will in a manner in which he or she is entitled to dispose of his or her property under that section; and
(b) whether or not the testator is a person to whom section 16 applies—
(i) by a subsequent valid will of the testator; or
(ii) by the testator executing a document in like manner as a will is required by part 2 to be executed that shows his or her intention to revoke the will or part; or
(iii) by the burning, tearing or otherwise destroying of the will or part by the testator, or by a person acting in the presence of and by the direction of the testator, with the intention of revoking the will or part.