Generally speaking, amendments must be witnessed in the same manner as the original trust, not necessarily by the same parties, and in accordance with the laws in your state.  I would urge you not to do this on your own but if you intend to do so here are some suggestions: if your wife is a beneficiary of the trust then I would not have her witness the amended document.  It just leaves less food for thought about undue influence if a witness is impartial and does not benefit in any way from the trust. I would add an additional witness for good measure even if only 2 are needed.  If the original document was notarized then notarize the amendment. Good luck.