If the proposed change to a will is simple (such as changing the name of the executor of the will), a codicil may be appropriate. A codicil shouldn't change the meaning of the overall purpose of the will or create any conflicts about who should get what property.
When you have many changes, it might be best to create a new will to track and preserve the overall meaning of the will.
Here are some things to consider when adding a codicil. It should:
Multiple documents, cancellations and reinstatements of parts of a will can get confusing so it may be simpler to draft a new will to make sure that your intent is clear. Destroying or writing "revoked" across the codicil document might not be enough to make intent clear even though the language is explicit.
Most of all, there should be little room for the will to be challenged by an upset heir when the meaning of the will is unclear.
When making a new will revoking a former one, the new will should specifically state that it's doing so to ensure that your intent that the most current will cancels any older versions. If a will or codicil doesn't mention that the updates revoke the previous version, then your intent on adding the codicil or making a new will altogether may be called into question and end up creating a lawsuit among the "wronged" beneficiaries.