I used to be the MD of a will-writing company, so I'm reasonably confident that I know my stuff here ;-)
Your will remains valid when your address changes. It also remains valid when your executors move home or die. It further remains valid when one or more beneficiaries move home or die (although what will happen to the entitlement of a deceased beneficiary under your will is going to depend upon the wording of the will and, if the will isn't explicit in its provisions relating to such a possibility, upon additional factors as well).
So you don't need to change your will. If you really want to though (although I can't see why you should), simply type out the content of your old will but changing the address shown to your new one. Then sign and date it in front of two adult witnesses (who must not be beneficiaries of your will) and get them to sign and date your will too. No cost is involved.