Packages for the release of the KDE Plasma Workspaces, Applications and Platform 4.8.5 are available for Kubuntu 12.04. You can get it from the Kubuntu Updates PPA until the packages are available in the official repositories.
Bugs in the packaging should be reported to kubuntu-ppa on Launchpad. Bugs in the software to KDE. To update, use the Software Repository Guide to add the following repository to your software sources list:ppa:kubuntu-ppa/ppa