How to change drupal checkbox as html structure

Copy and paste the below code in your template.tpl.php file in theme folder

function theme_checkbox($variables) {
  $element = $variables['element'];
  $element['#attributes']['type'] = 'checkbox';
  element_set_attributes($element, array('id', 'name', '#return_value' => 'value'));

  // Unchecked checkbox has #value of integer 0.
  if (!empty($element['#checked'])) {
    $element['#attributes']['checked'] = 'checked';
  }
  _form_set_class($element, array('form-checkbox'));

  return '<input' . drupal_attributes($element['#attributes']) . ' />';
}

Change theme_checkbox with your theme-name for example your theme name is prohcj then change it to prohcj_checkbox

and add your html structure inside return value. Example need to add before checkbox follow below code.

return '<span><input' . drupal_attributes($element['#attributes']) . ' /></span>';