Updating an older BBB

I tried to do this:
sudo apt-get install python-serial
Seems most of the links for apt update and upgrade are now broken for this OS version.

debian@ebb:~$ cat /etc/dogtag
BeagleBoard.org Debian Image 2018-10-07
debian@ebb:~$ uname -a
Linux ebb 4.14.108-ti-r136 #1stretch SMP PREEMPT Mon Jun 8 15:38:30 UTC 2020 armv7l GNU/Linux

I have a lot of stuff on this system. I realize I could probably copy over the /home folders to the network server and then copy them back. But there are all the other things like samba configuration, desktops etc.

Is there a way to update the OS in place without losing it all?