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 on the ellipses menu to the right of the question and choose Edit Question. 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 on the ellipses menu next to the question and choose Delete Question from Site. 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.