gistfile1.phtml

			$old_credits = array();
				$old_credits[] = get_metadata('post', 275142, '_media_credit', true);
				$old_credits[] = get_metadata('post', 275142, '_media_credit_2', true);
				$old_credits[] = get_metadata('post', 275142, '_media_credit_3', true);
				if ( $old_credits ) {
					$number = 0;
					$number_credits = count($old_credits);
					add_metadata( 'post', 275142, 'media_credit', $number_credits );
					add_metadata( 'post', 275142, '_media_credit', 'field_548e1e18a4b85' );
	
					foreach ( $old_credits as $old_credit ) {
						add_metadata( 'post', 275142, 'media_credit_' . $number . '_credit', $old_credit );
						add_metadata( 'post', 275142, '_media_credit_' . $number . '_credit', 'field_548e1e21a4b86' );
						$number++;
					}
				} 

				$old_credit_link_1 = get_metadata('post', 275142, '_media_credit_link', true);
				if ($old_credit_link_1 ) {
					add_metadata( 'post', 275142, 'media_credit_0_credit_link', $old_credit_link_1 );
					add_metadata( 'post', 275142, '_media_credit_0_credit_link', 'field_548e1e28a4b87' );
				}
				$old_credit_link_2 = get_metadata('post', 275142, '_media_credit_link_2', true);
				if ($old_credit_link_2 ) {
					add_metadata( 'post', 275142, 'media_credit_1_credit_link', $old_credit_link_2 );
					add_metadata( 'post', 275142, '_media_credit_1_credit_link', 'field_548e1e28a4b87' );
				}

				$old_credit_link_3 = get_metadata('post', 275142, '_media_credit_link_3', true);
				if ($old_credit_link_3 ) {
					add_metadata( 'post', 275142, 'media_credit_2_credit_link', $old_credit_link_3 );
					add_metadata( 'post', 275142, '_media_credit_2_credit_link', 'field_548e1e28a4b87' );
				}

  $my_post = array(
      'ID'           => 275142
  );

  wp_update_post( $my_post );