Irrevocable trusts are trusts that can be altered or revoked by the settlor.
Upon the death of the settlor of a revocable trust, the trust naturally becomes irrevocable because the potential revoker is dead.
Although often very similar to a will, revocable trusts do not require wills formalities. Under modern law, settlors can just opt in or out of the probate laws applying.
Revoking a trust is pretty similar to revoking a will. Tearing up the trust document is effective.
Trustees of revocable only owe fiduciary duties to the settlor. Beneficiaries have no rights.
Under the UTC, revocable trusts can be amended at any time by any method that manifests clear and convincing evidence of his intent to do so. UTC § 602(c).
A revocable trust is subject to the claims of the settlor's creditors during life and at death. UTC § 505(a)(3).
UPC § 2-804, revoking provisions to a former spouse, also applies to will substitutes.