code: public function regenerate_id( $delete_old = false ) {
  		if ( $delete_old ) {
  			delete_option( "_wp_session_{$this->session_id}" );
  		}
  		$this->session_id = $this->generate_id();
  		$this->set_cookie();
  	}
docs: Regenerate the current session's ID.
  
  @param bool $delete_old Flag whether or not to delete the old session data from the server.