If you want to archive a course just click the ... button and then "Move to archive" (see the below video).
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You can archive free courses as well as paid-for courses. But note that archiving paid-for courses does not mean you are "returning" them. Instead, if you have a course you want to return you can do so via email if it's within the 30-day guarantee period.

Another option is if you want to keep a course but not use it you can pause all chapters if you go into the Chapters page.