No, there is no paperwork to submit. Your premium will automatically be adjusted to the lower premium rate effective the first of the month in which your spouse turns age 65. For example, if you are paying $120 per month and your spouse turns age 65 on May 15th, your premium will be $60 per month effective May 1st.
If you are on pension deduction or automatic payment, the rate will automatically adjust effective the first of the month in which your spouse turns age 65.