If you are running any 6.4 or later release, click 'Check for Updates' on the Tools/Update OS page.
If you are running a pre-6.4 release, click 'Check for Updates' on the Plugins page.
If the above doesn't work, navigate to Plugins/Install Plugin, select/copy/paste this plugin URL and click Install:
Refer also to @ljm42 excellent 6.4 Update Notes which are helpful especially if you are upgrading from a pre-6.4 release.
BIOS: Especially if using Virtual Machines, we highly recommend keeping your motherboard bios up-to-date.
Bugs: If you discover a bug or other issue in this release, please open a Stable Releases Bug Report.
Version 6.6.3 2018-10-20
libvirt: version 4.7.0 (fix: virsh believes VMs are down when they are up)
Add the 'tss' user and group to keep libvirt from complaining
create /root/.docker folder symlink to flash /boot/config/plugins/dockerMan
webgui: Diagnostics: add totals in btrfs usage information
webgui: Docker: fix button color in alert messages
webgui: Update CPUvms.page help text
webgui: Code change to prevent CA from modifying system file
webgui: Fix container log size
webgui: Improve private docker registry support (correctly pulling and updating containers)
webgui: VM: upon editing vm allow adding vdisk after having none