You can make changes to your last will or revoke your last will at any time. However, there are some very important rules to follow. One way to make changes to a last will is to make a codicil, which is an amendment to a last will. Another way is to make an entirely new last will that states that the new last will revokes and takes precedence over any older last wills. A codicil is a separate document and must be signed and witnessed just like a regular last will. Because of these formalities, it may be easier to make an entirely new last will.
Do not make changes to, or put markings on, your last will after it has been witnessed and signed. This is essential. If you cross out someone's name or add other writing to a last will that has been signed, you risk making the whole last will invalid.