Unfortunately you can't change a Questions Type. If you made a mistake and you selected the wrong question type you have a couple of options:
If you haven't saved your question set yet, you can delete the original questions and add them again with the correct type.
If you have already saved your question set, those questions don't have the delete option. You can instead make them inactive and then just add the new questions.
If you are making the original questions inactive, then we would suggest you add the new question directly below the original and then cut and paste the question text down before making the original inactive.
