You can download Kubuntu in many ways. Choose the one that suits you the most.

Kubuntu 12.04 Release Announcement.

Regular Download

Download Kubuntu CD and USB stick images. For the desktop a 32-Bit version and a 64-Bit version are available. 
Download the Kubuntu installer to create your own installation CD or USB stick. The download process can take a while, depending on your connection speed (the file size is 700MB). 

BitTorrent

BitTorrent is a peer-to-peer download network that sometimes allows higher download speeds and provides more reliable downloads of large files. You will need to install a BitTorrent client on your computer in order to use this download method. 
You may then use one of the following links to download the Kubuntu images:

• Desktop CD, 32bit
• Desktop CD, 64bit
• Desktop DVD, 32bit
• Desktop DVD, 64bit
• Desktop Alternate CD, 32bit
• Desktop Alternate CD, 64bit

Read more about Alternate CD and Desktop DVD.

Burning a CD or creating an install USB stick

Kubuntu can be installed from a recordable CD (or DVD) or from a USB stick. Then it can be used as a regular operation system, or as a Live image which you can install Kubuntu from. For more information, see Burning ISO Howto andInstallation From USB Stick from the Ubuntu Community Documentation website.