Can I make changes to my will myself, or do I need a lawyer?

You should not simply write on the original will, since alterations made after a will has been signed and witnessed are not automatically valid unless they are executed with the same formalities, meaning signed and witnessed again in relation to the change, under the Wills Act 2007. The safer and clearer approach is to make a formal codicil, a separate document that amends specific parts of the will, or to make an entirely new will that revokes the earlier one, both properly signed and witnessed. Given the risk of ambiguity, especially when adding a beneficiary or changing executors, it is strongly advisable to use a lawyer or a trustee company to ensure the changes are valid and clearly expressed, and to avoid confusion or disputes among your beneficiaries after your death.