Note: copy and paste this code in functions.php of your current theme.

function custom_wpcsr_pickup_fields_callback( $fields ){
  /* Rename the fields */
  $fields['pickup_address1'] = 'Address 1';
  $fields['pickup_address2'] = 'Address 2';
  $fields['pickup_city'] = 'City';
  $fields['pickup_postcode'] = 'Postcode';
  $fields['pickup_country'] = 'Country';
  $fields['pickup_state'] = 'State';

  /* Add new field */
  $fields['new_field'] = 'New Field';  
  
  return $fields;
}
add_filter('wpcsr_pickup_fields', 'custom_wpcsr_pickup_fields_callback');