Как перезаписать в базе аватарку?

    class Userlk extends MY_Controller {
    public function avatar() {

            if(!$this->dx_auth->is_logged_in()) {
            show_404();
            // $this->load->helper('url_helper');
            // redirect('/', 'location');
            }

            $this->data['title'] = "Добавление аватарки";

            if($this->input->post('userSubmit')){

                //Check whether user upload picture
                if(!empty($_FILES['avatar']['name'])){
                    $config['upload_path'] = 'uploads/images/';
                    $config['allowed_types'] = 'jpg|jpeg|png|gif';
                    // $config['file_name'] = $_FILES['avatar']['name'];
                    $config['max_size'] = '50';
                    $config['max_width'] = '150';
                    $config['max_height'] = '150';
                    $config['remove_spaces'] = TRUE;
                    // $config['file_name'] = 'user_avatar';
                    // $config['overwrite'] = TRUE;



                    //Load upload library and initialize configuration
                    $this->load->library('upload',$config);
                    $this->upload->initialize($config);

                    if($this->upload->do_upload('avatar')){
                        $uploadData = $this->upload->data();
                        $avatar = $uploadData['file_name'];
                    }else{
                        $avatar = '';
                    }
                }else{
                    $avatar = '';
                }

                //Prepare array of user data
                $userData = array(
                    'name' => $this->input->post('name'),
                    'avatar' => $avatar
                );

                //Pass user data to model
                $insertUserData = $this->userlk_model->insertUserAvatar($userData);

                //Storing insertion status message.
                if($insertUserData){
                    $this->session->set_flashdata('success_msg', 'Аватарка добавлена!');
                }else{
                    $this->session->set_flashdata('error_msg', 'Какие-то проблемы с загрузкой аватарки, попробуйте ещё раз или обратитесь к администрации Retris.ru');
                }
            }

            $this->load->view('templates/header', $this->data);
            $this->load->view('userlk/avatar', $this->data);
            $this->load->view('templates/footer');
        }
}

Model:

 class Userlk_model extends CI_Model {

    public function __construct() {
        $this->load->database();

        $this->tableName = 'users_avatar';
        $this->primaryKey = 'id';
    }

public function insertUserAvatar($data = array()) {
        if(!array_key_exists("created",$data)){
            $data['created'] = date("Y-m-d H:i:s");
        }
        if(!array_key_exists("modified",$data)){
            $data['modified'] = date("Y-m-d H:i:s");
        }
        $insert = $this->db->insert($this->tableName,$data);
        if($insert){
            return $this->db->insert_id();
        }else{
            return false;    
        }
    }


    public function getUserAvatar() {

        return $this->db
        ->get_where("users_avatar", array('name' => $this->dx_auth->get_username()))->result();
        // ->get('users_avatar');
        // return $query->row_array();

    }

}

view:

<?php echo $this->session->flashdata('success_msg'); ?>
<?php echo $this->session->flashdata('error_msg'); ?>
<form role="form" method="post" enctype="multipart/form-data">
    <div class="panel">
        <div class="panel-body">
            <div class="form-group">
                <label>Загрузить</label>
                <input class="form-control" type="file" name="avatar" required="" />
            </div>
            <div class="form-group">
                <label>Ваше имя</label>
                <input class="form-control" type="text" name="name" value="<?php echo $this->dx_auth->get_username(); ?>" />
            </div>
             <div class="form-group">
                <input type="submit" class="btn btn-warning" name="userSubmit" value="Добавить">
            </div>
        </div>
    </div>
</form>