Please review the help article How do I edit a quiz question?.
If you are looking for information on how to edit question settings, please review the help article How do I apply settings for an entire Homework activity?.
If you see a warning message like the one pictured below that prevents you from editing your Homework assignment, you can still edit the content of questions, just not the settings. Please review the help article How do I edit the content of a question in a locked Homework assignment? for more information on how to do this.