We license our course content (including this very sentence) with a Creative Commons BY-SA license, which means that anybody can reuse or remix content so long as they attribute us (BY) and share their derivative work with the same license (SA=Share Alike). You are free to choose any license that you like: Creative Commons offers a number of licenses, and there are alternative licenses as well. To change your course license, you need to update text in two places: the website footer and the README file.
You may also have noticed a LICENSE file in your repository: this license is for Course-in-a-Box software, not for the content that you create. Do not edit the LICENSE file when changing the content license.