To update software in Raspbian, you'll need to use the apt tool in a terminal window. Open the terminal from the taskbar or application menu:
First, update your system's package list by entering the following command:
sudo apt-get updateNext, upgrade all your installed packages to their latest versions with the command:
sudo apt-get dist-upgradeGenerally speaking, doing this regularly will keep your installation up to date, in that it will be equivalent to the latest released image available from raspberrypi.org/downloads.
However, there are occasional changes made in the Foundation's Raspbian image that require manual intervention, for example a newly introduced package. These are not installed with an upgrade, as this command only updates the packages you already have installed.
The kernel and firmware are installed as a Debian package, and so will also get updates when using the procedure above. These packages are updated infrequently and after extensive testing.
When running sudo apt-get dist-upgrade, it will show how much data will be downloaded and how much space it will take up on the SD card. It's worth checking with df -h that you have enough free disk space, as unfortunately apt will not do this for you. Also be aware that downloaded package files (.deb files) are kept in /var/cache/apt/archives. You can remove these in order to free up space with sudo apt-get clean.
Upgrading an existing Jessie image is possible, but is not guaranteed to work in every circumstance. If you wish to try upgrading a Jessie image to Stretch, we strongly recommend making a backup first — we can accept no responsibility for loss of data from a failed update.
To upgrade, first modify the files /etc/apt/sources.list and /etc/apt/sources.list.d/raspi.list. In both files, change every occurrence of the word jessie to stretch. (Both files will require sudo to edit.)
Then open a terminal window and execute:
sudo apt-get update
sudo apt-get -y dist-upgradeAnswer 'yes' to any prompts. There may also be a point at which the install pauses while a page of information is shown on the screen – hold the space key to scroll through all of this and then press q to continue.
Finally, if you are not using PulseAudio for anything other than Bluetooth audio, remove it from the image by entering:
sudo apt-get -y purge "pulseaudio*"
If moving to a new Pi model (for example the Pi 3B+), you may also need to update the kernel and the firmware using the instructions above.