libraries/class-wp-session.php
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();
	}
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();
	}
Regenerate the current session's ID.

@param bool $delete_old Flag whether or not to delete the old session data from the server.