You can manage the form with the Drupal navigation: Structure > Webforms
If you change something in here please be aware of the fact that element "main_container" is required for the 2 column layout of the form.
The sections on the second level are columns for the grid layout. If you want to have more or want to remove them please use the classes which are already used from the theme. Take the screenshots as a reference.
You can edit each input field and set for example minimum or maximum values & more.