The status of your estate -- and your relationship with various heirs and beneficiaries -- changes over time. After creating a will, you might get married or divorced. You might have additional children or grandchildren. The ways in which your relationships can change are almost unlimited, as are the reasons you might want to edit a will. To make valid changes to your will, however, you simply can't edit the document and call it a day.
How you must revoke your old will depends on the state your will was created in and the state where you will be creating your new will. In most cases, you can destroy the original copy of the old will, create a valid and executed new will that postdates the old will, or make documented changes to the old will.
Destroying the old will usually means shredding it, but you could also burn it or otherwise destroy the document. In most cases, you can require that someone else destroy the document. The original has to be destroyed; destroying a copy doesn't invalidate the will. If you only want to remove a single provision from the will, it's usually not enough to simply cross it out.
Creating a new -- and legally valid -- will causes any older will to be revoked. It's probably still a good idea to destroy old copies of wills, though. The existence of multiple wills can cause disputes during the probate process.
You can edit a will by making witnessed and signed changes to the document. The new document is referred to as a codicil. You can create a codicil to add or remove heirs from a will or make other major changes. Changing a will or creating a new will can have long-lasting legal ramifications, making it a good idea to consult a legal professional to ensure you are maintaining a solid estate plan with your changes.
Source: FindLaw, "How to Revoke a Will," accessed Jan. 08, 2016