Unlink update image codeigniter

hallo bro..

saya mau hapus gambar lama setelah saya update gambar baru. saya sudah tambahkan unlink, tetapi gambar lama tidak terhapus.

controller :

public function Update()
    {

      $id = $this->input->post('id');

      $nama               = $this->input->post('nama');

      if($_FILES['image']['name']!="")
            {
      $config['upload_path']   = './image/';
      $config['allowed_types'] ='gif|jpg|png|jpeg|jpe|pdf|doc|docx|rtf|text|txt';
        $this->load->library('upload', $config);
        if($this->upload->do_upload('image')){
                $uploadData = $this->upload->data();
                $image = $uploadData['file_name'];
            }else{
                $image= '';
            }
        }else{
            $image = '';
        }

        $data = array(
          'nama'   => $nama,

          );
if($image != ''){
          $data['image'] = $image;
          unlink("./image/$row->file_name");
      }

        $this->model_user->update_user($data,$id);
    }

Model :

public function update_user($data, $id)
    {
        $this->db->where('id', $id);
        $this->db->update('tabel_user', $data);
        return TRUE;
    }

mohon bantuannya bro.

Terima Kasih.