You can opt-out of Course Material Access in Canvas via the "My Shelf" link under the "Account" button in the sidebar.
Detailed instructions for opting out of your course materials can be found here and in the video below.
Note: You must opt out before the Add/Drop deadline. You can view the semester deadlines here under the section titled "Last day to DROP without "W" grade and 100% tuition refund on LoboWeb.".