Legal Question in Wills and Trusts in Illinois

Certainly you can. Any changes to a Will must be signed and witnessed as required by Illinois law -- you need 2 disinterested witnesses. Usually it's best to incorporate the changes you want into a new Will. Best bet is to contact an estate planning attorney.

An amendment to a will is called a codicil and must be signed with the same formality as a will. I recommend you meet with a reputable attorney to review your current will and discuss your intentions. Wills are usually drafted to avoid having to revise them with each slight change in circumstances, but after forty years I would expect that revisions would be likely. More importantly, there may be estate planning that can be done that would save your estate money or avoid probate if appropriate. Often, a new will is easier and better than a codicil. An attorney will have an easier time drafting what you want in a simple will than to make references and substitutions of language to an old will. Also, there is less likelihood of confusion and error.

Go see a lawyer.