1. Check Kernel version
uname -a /opt/vc/bin/vcgencmd version
2. Download rpi-update script & Run
sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update
sudo chmod +x /usr/bin/rpi-update
sudo rpi-update
3. Reboot
sudo reboot
uname -a /opt/vc/bin/vcgencmd version
sudo wget http://goo.gl/1BOfJ -O /usr/bin/rpi-update
sudo chmod +x /usr/bin/rpi-update
sudo rpi-update
sudo reboot