All subscription charges are final and cannot be reversed.
If you cancel in the middle of a billing period, you will not be charged in the future, but there are no refunds for partially used time periods, even if it is a single day.
For more information, please refer to the Payments of Fees and Taxes portion of Shopify's Terms of Service.
Before committing to a yearly subscription, we recommend starting with the monthly plan to determine if the Pro Plan subscription for Theme Updater suits your needs