Help to save data from a field to the database without creating a new record?

Question

I have the following table in the system:

When I enter the Status and click update it creates another record in the database.

Follow the record in the comic book. I would like it to only record the status in the registry with the id in question!

Code:

    <div class="tabs-vertical-env">

        <ul class="nav tabs-vertical">
        <?php
            $classes = $this->db->get('class')->result_array();
            foreach ($classes as $row):
        ?>
            <li class="<?php if ($row['class_id'] == $class_id) echo 'active';?>">
                <a href="<?php echo site_url('admin/academic_syllabus/' . $row['class_id']);?>">
                    <i class="entypo-dot"></i>
                    <?php echo get_phrase('class');?> <?php echo $row['name'];?>
                </a>
            </li>
        <?php endforeach;?>
        </ul>

        <div class="tab-content">

        <?php
            echo form_open(site_url('admin/upload_academic_syllabus/'.$exam_id.'/'.$class_id.'/'.$section_id.'/'.$subject_id));
            ?>

            <div class="tab-pane active">
                <table class="table table-bordered responsive">
                    <thead>
                        <tr>
                            <th>#</th>
                            <th><?php echo get_phrase('title');?></th>
                            <th><?php echo get_phrase('description');?></th>
                            <th><?php echo get_phrase('subject');?></th>
                            <th><?php echo get_phrase('uploader');?></th>
                            <th><?php echo get_phrase('date');?></th>
                            <th><?php echo get_phrase('file');?></th>
                            <th></th>
                            <th>Status</th>
                        </tr>
                    </thead>
                    <tbody>

                    <?php
                        $count    = 1;
                        $syllabus = $this->db->get_where('academic_syllabus' , array(
                            'class_id' => $class_id , 'year' => $running_year
                        ))->result_array();
                        foreach ($syllabus as $row):
                    ?>
                        <tr>
                            <td><?php echo $count++;?></td>
                            <td><?php echo $row['title'];?></td>
                            <td><?php echo $row['description'];?></td>
                                                            <td>
                                <?php
                                    echo $this->db->get_where('subject' , array(
                                        'subject_id' => $row['subject_id']
                                    ))->row()->name;
                                ?>
                            </td>
                            <td>
                                <?php
                                    echo $this->db->get_where($row['uploader_type'] , array(
                                        $row['uploader_type'].'_id' => $row['uploader_id']
                                    ))->row()->name;
                                ?>
                            </td>
                            <td><?php echo date("d/m/Y" , $row['timestamp']);?></td>
                            <td>
                                <?php echo substr($row['file_name'], 0, 20);?><?php if(strlen($row['file_name']) > 20) echo '...';?>
                            </td>
                            <td align="center">
                                <a class="btn btn-default btn-xs"
                                    href="<?php echo site_url('admin/download_academic_syllabus/' . $row['academic_syllabus_code']);?>">
                                    <i class="entypo-download"></i>
                                </a>
                                <a href="#" class="btn btn-danger btn-xs"
                                    onclick="confirm_modal('<?php echo site_url('admin/delete_academic_syllabus/' . $row['academic_syllabus_code']);?>');">
                                    <i class="entypo-trash"></i>
                                </a>
                            </td>
                            <td>
                    <input type="text" class="form-control" name="status">
                        </td>
                        <td>        <center>
        <button type="submit" class="btn btn-success" id="submit_button">
            <i class="entypo-check"></i> Atualizar status
        </button>
    </center>
                        </tr>
                    <?php endforeach;?>

                    </tbody>
                </table>

    <?php echo form_close();?>
            </div>

        </div>

    </div>

</div>

Controller Code:

    // ACADEMIC SYLLABUS
function academic_syllabus($class_id = '')
{
    if ($this->session->userdata('admin_login') != 1)
        redirect(site_url('login'), 'refresh');
    // detect the first class
    if ($class_id == '')
        $class_id           =   $this->db->get('class')->first_row()->class_id;

    $page_data['page_name']  = 'academic_syllabus';
    $page_data['page_title'] = get_phrase('academic_syllabus');
    $page_data['class_id']   = $class_id;
    $this->load->view('backend/index', $page_data);
}

function upload_academic_syllabus()
{
    $data['academic_syllabus_code'] =   substr(md5(rand(0, 1000000)), 0, 7);
    if ($this->input->post('description') != null) {
       $data['description'] = $this->input->post('description');
    }
    $data['title']                  =   $this->input->post('title');
    $data['class_id']               =   $this->input->post('class_id');
    $data['subject_id']             =   $this->input->post('subject_id');
    $data['uploader_type']          =   $this->session->userdata('login_type');
    $data['uploader_id']            =   $this->session->userdata('login_user_id');
    $data['year']                   =   $this->db->get_where('settings',array('type'=>'running_year'))->row()->description;
    $data['timestamp']              =   strtotime(date("Y-m-d H:i:s"));
    //uploading file using codeigniter upload library
    $files = $_FILES['file_name'];
    $this->load->library('upload');
    $config['upload_path']   =  'uploads/syllabus/';
    $config['allowed_types'] =  '*';
    $_FILES['file_name']['name']     = $files['name'];
    $_FILES['file_name']['type']     = $files['type'];
    $_FILES['file_name']['tmp_name'] = $files['tmp_name'];
    $_FILES['file_name']['size']     = $files['size'];
    $this->upload->initialize($config);
    $this->upload->do_upload('file_name');

    $data['file_name'] = $_FILES['file_name']['name'];

    $this->db->insert('academic_syllabus', $data);
    $this->session->set_flashdata('flash_message' , get_phrase('syllabus_uploaded'));
    redirect(site_url('admin/academic_syllabus/' . $data['class_id']), 'refresh');

}