There is only difference of desktop environment in Ubuntu and Kubuntu.
You can use Kde desktop environment in Ubuntu and turn it into Kubuntu , you dont need to remove Ubuntu
Open terminal by pressing Crtl + Alt + T and then execute following command one by one :
sudo apt-get update
sudo apt-get install software-properties-kde
sudo apt-get install kubuntu-desktop
If you still want to remove Ubuntu and Install Kubuntu.
Burn iso image(kubuntu 14.04.2.iso ) into a DVD and Visit this site for step by step process of installing Ubuntu (or Kubuntu)