问如何在上传pdf文件的同时增加大于5mb的大小

EN

public function question_upload() {           
    $this->form_validation->set_rules('examname', 'Select Exam Type', 'required');
    $this->form_validation->set_rules('assignment', 'Subject Name', 'required');
    $this->form_validation->set_rules('question', 'Content Name', 'required');
    $this->form_validation->set_rules('subcontent', 'Sub Content Name', 'required');
    if (empty($_FILES['picture']['name'])) {
    $this->form_validation->set_rules('picture', 'Pdf', 'required');
    }
    if ($this->form_validation->run() == FALSE) {
    $data['h'] = $this->Faculty_Model->faculty_QuestionDisplay();
    $data['studentAnswer'] = $this->Faculty_Model->student_Question();
    $this->load->view('index1', $data);
    } else {
    if (!empty($_FILES['picture']['name']))         
    $config['upload_path'] = 'uploads/files/';
    $config['allowed_types'] = 'jpg|jpeg|png|gif|pdf';
    $config['file_name'] = $_FILES['picture']['name'];   
    $this->load->library('upload', $config);
    $this->upload->initialize($config);
    if ($this->upload->do_upload('picture')) {
    $uploadData = $this->upload->data();
    $picture = $uploadData['file_name'];
    } else {
    $picture = '';
    }
    } else {
    $picture = '';
    }
    $userData = array(
    'datee' => $this->input->post('datee'),
    'examname' => $this->input->post('examname'),
    'assignment_name' => $this->input->post('assignment'),
    'question   ' => $this->input->post('question'),
    'subcontent' => $this->input->post('subcontent'),
    'pdffile' => $picture
    );
    $this->Faculty_Model->faculty_Questioninsert($userData);

    $this->session->set_flashdata('success_msg', 'User data have been added successfully.');
    redirect('welcome/index1');
    }
    }