Prob. Code 15401 sets out a statutory procedure for revocation of a revocable trust under which the trustor need only sign a revocation and deliver it to the trustee.  The trustor may avail himself of this statutory procedure unless the revocable trust expressly states that a different method of revocation set out in the trust instrument is the exclusive means by which the trust may be revoked.  Section 15401 governs both the method of revocation and who is authorized to revoke the trust.  So the trustor validly invoked the statutory means of revocation even though the trust set out a different procedure requiring a signature of the attorney who had drafted the original trust instrument.