Go to www.gov.uk/register-to-vote

Fill in your name, address, date of birth and a few other details. You’ll also need your national insurance number, which can be found on your national insurance card, or in official paperwork such as payslips, or letters about benefits or tax credits.
You will receive a letter from Milton Keynes Council to confirm that you are registered or if you need to provide further information.
To find out more visit Your Vote Matters information provided by Gov.UK