Release details https://docs.armbian.com/Release_Changelog/
Upgrading your Armbian to v19.11.y
This upgrade is changing kernel branch names and first upgrade is not done via regular apt-upgrade process, but you have to login as root or get super user privileges with sudo su. Than do the following:
apt update
apt upgrade
armbian-config
-> system -> Other -> select either legacy or current with v19.11.3
Choose latest version of 19.11.x