CodeIgniter 3会话安全性

I have a question about security in netbeans. Generally I have problems understanding the session. I think the session value user can change and when my code view is this:

$this->session->set_userdata('uid', $result['uid']);
                    $this->session->set_userdata('uname', $result['uname']);
                    $this->session->set_userdata('uemail', $result['uemail']);
                    $this->session->set_userdata('privilages', $result['privilages']);

I send to session privates data like userid or privileges. It is possible to change value of session and if is possible, how I can make my system more secure?