Note: To edit questions in a YuJa video quiz, you must be the owner of the video.

Log in to YuJa at https://wccnet.yuja.com/, Hover over the video that contains the quiz and click More...
In the Media Details window, click Quizzes on the left, then click Edit on the quiz.
Choose if you'd like to edit the existing quiz or create a copy and edit a new version. Most likely you'll want to click Edit this Quiz.
Now on the edit screen, you can add questions or adjust settings just like when you created the quiz. But to edit existing questions, you can click the question in the Question List.
Make any adjustments necessary, then click Save.
When finished, click Save on the quiz.