Within the editing page, click 'Edit Form' on the left-side menu.
To edit a form field, click the blue 'Edit' button to the right of the field, in the column called 'Options'. To delete a form field, click the red 'X' that is also to in the 'Options' column to the right of the field. To sort your form fields, use the arrows under 'Sort' to click and drag them up or down to where you want them.
Make sure to save your changes by clicking the green 'Save' button to the top right or bottom of this page.