To change your Will, you cannot simply write changes on an existing Will as such alterations are assumed to have been made after the original Will was executed and will not form part of the Will. It may even invalidate the existing Will.
The only way a Last Will and Testament can be legally changed is by:
making a codicil to the existing Will, or
making an entirely new Will.
A codicil is a 'supplement' to an existing Will that may make a small change but refers to the original Will itself ensuring that Will still remains valid and enforceable. The codicil, for example, may be used to add an additional Executor to the current Will.
A codicil is a legal document and so must be signed, dated and witnessed in the same way as a Will. It must be on a separate document and reference the original Will and those clauses that are being changed and those which are not. The requirement in terms of capacity to make the Codicil and understand the value and extent of your estate are the same as with the making of a Will.
Legal advice should in addition always be obtained when making a codicil to ensure those parts of the original Will that you want to remain intact do; and to ensure the codicil has the required effect.
After the codicil is executed, it should be stored with the original Will in a safe place. It is recommended that codicils are numbered, so that executors will know how many documents to consult alongside the Will. It is possible to make more than one though again not considered advisable.
You must also ensure that you do not attach the codicil(s) to the Will, as doing so would potentially invalidate both documents.
A new Will is always considered best practice where any change to an existing Will is required however, certainly where the change is significant or complex. Further, if you wish to make a number of changes, again, it is advisable to make a new Will.
Law firms will make a charge whether you are making a new Will or a codicil and as the requirements for making a codicil are the same, it is advised that a new Will should always be made where changes are required. Our service at Bequeathed provides a new straightforward Will for free but where a codicil is preferred we can refer you to one of our partner law firms for a free 30 minute consultation where your options can be considered further and a way forward agreed.