As of now Android 4.4 kitkat is only available for few Nexus devices officially. But there are huge number of devices already running on latest Kitkat Android update using the Custom ROMs. Also most of the major smartphone brands like Samsung, Sony, HTC, etc have already started working to port the OS for their latest or recent flagship smartphones or Tablets. However older devices like HTC HD2 may not receive the same officially as it is bit old launched long time ago.
Hence, if you are the one holding this smartphone and want to taste out the new Kitkat, you can get it using a custom firmware named SlimKat 4.4. It is a light weight firmware working great on HD2. You can download the same from this page and install it on your system. In case you are not aware of the installation process, check on out forums. If you have any more question about this ROM or installation, feel free to ask using the comment box.