A supplement to a will, consisting of revisions, additions, or alterations made after the will has been made, is known as a codicil. The codicil must be executed (signed, witnessed, etc.) in the same manner as the will being amended. Corrections should not be made in a will by erasures, insertions, or cross-outs. All corrections or other changes should be made by codicil and in many cases it may be preferable to execute a new will.
If a new will is made, it should state that all prior wills are revoked. It may also be desirable to physically destroy a previous will to avoid any possible confusion later.