I decided to take the plunge and update my laptop to the latest Debian release as I was still running Jessie.
My desktop PC has been running Stretch since it was released but it was a clean install on a new hard drive so didn’t have the possibility of a failed upgrade.
Full upgrade using the apt-get dist-upgrade option went relatively smoothly bar a couple of dependency issues which I resolved by removing the affending packages as they were not that important (just KDE libraries). All in it took about 2.5 hours to finish the upgrade, including reading/research and backing up important files. Backups are good!
I followed (or at least read) the instructions from Debian upgrade guide but the basics are:
Make sure your current system is up to date
(if there are upgrades available)
(optional, just clears out downloaded files used to install/upgrade)
Change your apt sources file (/etc/apt/sources.list) to point to new release. Change all instances of jessie in the sources.list file to stretch, save then rerun apt-get update to update the new release files.
Run apt-get upgrade again to upgrade any installed packages (this may throw up list of files no longer needed as well). After these are upgraded you can run the dist-upgrade command to upgrade to the latest release.
Once this is finished you are now running the latest release which you can test by looking at the content of the file /etc/debian_version which in my case is now 9.2. you can check the kernel version as well by running uname -a from the terminal which gives me
Linux debian 4.9.0-4-amd64 #1 SMP Debian 4.9.51-1 (2017-09-28) x86_64 GNU/Linux
This is just a quick and dirty run through of the basic process i would suggest you read the full upgrade instructions from the Debian website guide to upgrading to fully understand the issues you may have (oh and make a backup if you have important data on the drive). Backups are good!