I thought that upgrading to 18.04.1 would give me KDE Plasma 5.13, having read this page, but thanks to the comments here I realised that I already have 18.04.1. I don't see any notification from the Updates widget about a newer version of Plasma though. Why is that? Can I get the latest version?
https://community.kde.org/Neon/BionicUpgrades isn't meant for users of Kubuntu. It's meant for users of KDE neon which isn't supported at Ask Ubuntu.
If you're on Kubuntu 18.04, please note that Plasma 5.12 is regarded as LTS which means you'll get updates only to 5.12 and you won't get updated to Plasma 5.13 or higher during the life of Kubuntu 18.04.
Please monitor https://kubuntu.org/news/ or https://www.kubuntuforums.net/forumdisplay.php/30-Kubuntu-Announcements for news on availability of Plasma updates for Kubuntu 18.04..
I see your question is pointless now, as you were already in 18.04.01. You might consider deleting it.
Or, for the record, in order for it to have its answer.
As said in a comment by @Kulfy:
sudo apt-get update sudo apt-get upgrade
You can also use
(if you have that installed)
You can verify your version with
But, as said in @DKBosse's answer, you will not get Plasma 5.13 in this way, only updates to 5.12.
(Testing 5.13 in Neon a few months ago it seemed unstable to me.)