I think I am using Jessie. Not sure why. I just have it up to date with the latest flight aware software. 3.6.3. Didn’t know that could be changed. Thought it was set by FlightAware.
Normally (don’t do it!) you would run
sudo apt-get update sudo apt-get dist-upgrade
To get the next major milestone of the operating system.
But there was a problem with the old piaware sd-card image resulting in errors when doing that update.
So you are encouraged to download the latest piaware sd-card image.
After that point even if the major operating system version changes again after stretch you should be able to just use these commands to upgrade.
But it is not strictly necessary, jessie can work fine as well.
If you try to follow some instructions like or install stuff, it might be meant for stretch and not work correctly.
To find your OS verison, use following command:
See below the output generated when this command was issued on Raspbian Jessie.
PRETTY_NAME=“Debian GNU/Linux 8 (jessie)”