
Kubuntu allows themes to be changed simply. Go to the Kickoff Application Launcher (K Menu)
Click on Computer
Open System Settings.
In the Worksapce Appearance and Behaviour section, click on
From here, it's possible to choose from the list of installed themes.
To install a new theme, click on the button at the bottom right.
From here, pick the source and run a search for the desired theme.
Once the theme is downloaded and installed, it can be picked from the list of installed themes.