As life circumstances change (births, marriages, divorces, and deaths), it may become necessary to make changes to your will.  If an estate plan is not kept up-to-date, it can become useless.  You can make changes using a codicil -- an amendment to the will -- or by creating a new will.  Creating a new will is usually the best option.

While it may be tempting to just take out a pen and make changes by hand, this is not recommended. Changes will not be effective unless you use the same formalities as you did when you signed the will. And depending on state law, changes made by hand on the will may void the will altogether. If you sign your name to handwritten changes and have the changes witnessed, it is possible a court will find that the changes are valid, but there is no guarantee and there are likely to be delays with the court while your final wishes are sorted out.

If you have small changes to make to your will (e.g., changing your executor or updating a name that has changed), a codicil may be appropriate. The same rules for wills apply to codicils, which means the codicil should be dated, signed, and witnessed. Always keep a codicil with the will so your personal representative can find it easily.

If you have significant changes to make to your will (e.g., adding a spouse or removing a beneficiary) or have more than one change, it is generally better to update your will rather than write one or more codicils. The updated will should include a date and a clear statement that all other previous wills and codicils are revoked. 

Before you make any changes to your will, you should consult with your attorney.