I've quite struggled on this (on several successive topics) (more than it should have been), due to this poor support of online sources over time, that have lead on my side to a lot of experiments trying to repair / correct the Jessie archive URL (hence a lot of waste of time).
Indeed, i've in the end upgraded my previous Jessie armbian to Stretch without reinstalling.
Sadly i haven't taken any notes about it ...
Basically i did, as far as i can remember (after the unsuccessful experiments while still being on Jessie) :
- upgraded what i could while still being on jessie + removed a few packages to clean up the system
- changed my /etc/apt/sources.list to :
- put in comment the content of /etc/apt/sources.list.d/armbian.list and hypriot.list, as it seems they are not available anymore (it's the only two additional sources files i had)
- upgraded the whole system with
- resolve several issues, i don't remember all of them (and maybe there are not only related to the upgrade process, but rather to the pine64 support for Stretch). For example i had a lot of issues about the wlan (with debug messages that were printed all the time due to two wlan cards being now discovered ... took some time to figure), now i have (i think it's the most relevant part but i did a lot of other things like disabling IPv6) :
to be added in /etc/network/interfaces in order to disable the second wlan1 interface (and i'm using wlan0 in auto/dhcp mode) (as seen here : https://github.com/ayufan-pine64/linux-build/blob/master/package/root/etc/network/interfaces.d/wlan1)
And for IPv6, in /etc/sysctl.conf :
In the end i still have a running armbian Stretch on my PINE64 box (with octoprint).
Fore reference, my PINE64 board has been bought during the kickstarted and is a PINE A64 model (with mem 2GB).
Good luck in your upgrade process.