Alter the user registration form
Here is the right code:

/**
 * Implements hook_form_FORM_ID_alter().
 */
function &lt;your_module&gt;_form_user_register_form_alter(&amp;$form, \Drupal\Core\Form\FormStateInterface $form_state, $form_id) {
  $form['account']['name']['#title'] = t('First and last name');
  $form['account']['name']['#description'] = t("Rewrite this about spaces, periods (.), hyphens (-) and apostrophes (').");
}


feel free to ask :)
have fun!