Updating the GPU firmware on Debian/Raspbian
You can update the firmware using rpi-update by Hexxeh. On Raspbian, you can install it by running
sudo apt-get install rpi-update
To update the software, run
sudo rpi-update
Updating userspace and kernel Software on Debian/Raspbian
sudo apt-get upgrade
If there are any errors, you can try updating the database first by running
sudo apt-get update
Source: stackexchange