How Can I Extend Session Time

[eluser]mTuran[/eluser]
Hi, in my application users login then i set some variables to session like that:

Code:

$user = array(
   'id' => $user[0]->id,
   'username' => $user[0]->username,
   'fullname' => $user[0]->fullname
);

$this->CI->session->set_userdata($user);

i use ci session library and hold data in database but there is time limit(7200) which is setted in config.php. if user stay page more than 2 hours, user will logout automatically because of session expire. i am waitting your recommendations. Thanks you.