Since you have an A-B trust, you'll need to split the trust into 2 trusts. Since A-B trust transfers are complex, you may need the help of an attorney. You'll need to review the part of the original trust agreement that contains the terms for your survivor's trust. After the death of the decedent, the trustee is required to obtain a tax identification number for each trust other than a grantor trust as defined in federal income tax laws. The Decedent?s Trust and any Marital Trust are irrevocable trusts and will each require a tax identification number. Each year, the trustee must file a fiduciary income tax return ,IRS Form 1041 ,for each irrevocable trust, providing a sch K-1 to each income beneficiary If you have a traditional trust, you need to review your original living trust agreement before you move to change it. Your spouse's death will change the way the trust's assets are distributed upon your death if your spouse was a beneficiary. You'll also need to decide who you want to name as a successor trustee if your spouse was one of the successors in the original agreement.