Trust Amendment

I have been instructed to amend a trust schedule where the trust property in a Discretionary Settlement has now changed. The trustees are selling the current property held under the trust and are purchasing a new one. The conveyancing solicitors are insisting that the schedule in the trust deed is updated to reflect the new property details so that this can then be registered at the land registry.
Would a trustee resolution to sell the current property held and purchase a new one suffice or would I need to prepare an amended trust deed of some kind?
Thanks