Though HTC Desire is an old phone released back in 2010 in Froyo (Android 2.2) days but you can still install a lot of custom ROMs on it to enhance its capabilities.
And now you can install latest Android version (Android Kitkat 4.4.2) on your Desire.
The ROM has been developed by an xda recognized developer LaidbackNikez. Its still a pre-alpha version, so some functions might not work. But you can still have a look of Android Kitkat 4.4.2. Keep visiting the xda link to get updated regarding releases of Kitkat ROM.
Now lets get to some of the pre-requisites of installing Kitkat on Desire.
Things Required to Install Kitkat on Desire:
To install this Custom ROM you require:
A rooted HTC Desire/ or HTC Phone.
Appropriate Recovery (lets say CWM) installed.
A brief knowledge of Flashing Custom ROMs through recovery.
Important To Know
If you don’t know what is Rooting and what are the benefits of Rooting, I have written a separate article for its knowledge:
Steps to Install Evervolv Kitkat 4.4 ROM:
First you have to download the ROM from following this direct link or go to nikez website and manually select the latest release of Evervolv Turba for Kitkat. You can also visit official XDA page for this ROM by following this link.
Copy the downloaded file (name similar to ev_bravo-4.0.0p2-turba.zip) to your memory card and boot into recovery by pressing Volume down and Power key simultaneously, and then selecting Recovery.
Select Wipe Data / Factory Reset.
Select Wipe Cache
Select Install ZIP from SD Card.
Navigate to ev_bravo-4.0.0p2-turba.zip file and confirm to flash the ROM.
Reboot the phone and enjoy Kitkat experience on your Desire.
I am always there to help you out if you have got some confusion in your mind. You can also read original XDA article to get official support from the developer. (Link mentioned above)