Request that the trustee make your desired alterations in the trust with a series of amendments, which the trustee must draw up, sign and append to the original trust document. The trustee must hold the authority to make these changes through a power of appointment, created within the original trust documents; the changes may not infringe on the rights of the trust beneficiaries. Alternately, a trustee may petition a court to modify the trust for good cause; for example, if new circumstances would defeat your original intention for the trust.
Appoint, or have appointed, a "trust protector," who has the authority to review the trust for any necessary changes as the law and your personal circumstances vary. A trust protector may propose alterations to the trustee, who then may make amendments within the authority he holds in the original trust.
Request the trustee and all beneficiaries sign written consent forms that agree to your proposed changes in the trust. The changes in the trust must be approved in probate or family court with jurisdiction over the matter.
Create a new trust with the new terms that you wish to implement, and request that the trustee transfer assets from the old trust, or sell them, to the new one. State law must permit such an action, which may not infringe the rights of the original beneficiaries. If real estate, stock, or other investments are sold or liquidated, then income and/or gift taxes will be due on any profit from the sale.