To get the latest KDE software updates, you simply need to enable the 2 Backports Channels.
Just start “Update Manager” and select “Software sources” from the “Edit” Menu (as can be seen here before enabling the Backports channels):
Then TICK both maui-xenial-backports and maui-xenial-backports-neon, so it looks like this:
That’s it!
If you like your current system and want to keep it absolute stable, you can at any time UNTICK those two channels again and that way stay on a certain software selection for as long as you want to.