A change or addition to a will is called a codicil.
By his will, made in 1852, with a codicil dated February 1859, his property, with the exception of some small bequests, was devised to the above-mentioned institution at Berlin.
I suggest you see the Solicitor who originally drew up the will to make the codicil for you.
A testator can alter a will without scrapping it, by preparing a codicil.
Legacies are simple to put into effect by adding a codicil or making a revision to your will.