To make changes to your User Form questions, first navigate to the User Form (instructions for this can be found in Part 2 of the Getting Started Guide).
To edit an existing User Form question, click the orange ellipsis (...) button to the right of the question and select "Edit Question" from the menu that appears. You will then be able to make changes to any property of that question, with the exception of the question type. To change the question type, you will need to create a new question with the desired type and delete the original one.
To delete a question, click the ellipsis (...) button beside the question and select "Delete Question from Site" from the menu. Note that this will permanently delete the question and all responses to it from your site, which cannot be undone!
Details on creating questions can be found in Part 2 of the Getting Started Guide.