Android 4.2.2 Jelly Bean is already ported for almost all high end devices but now it’s time for devices like HTC Desire. Thanks to XDA Senior Member vijendrahs bringing out CM 10.1 JB 4.2.2.

cm10desire

What is working:
CyanogenMod settings
Soft-Nav
Mobile Network
Calls
3G/Data
Wifi
WifI Tether
Bluetooth
GPS
Sound
USB
Camera
Video Recording (Still choppiness, use MX Player with S/W decoder for playing)
HWA
Video Playback without any flickering
Flash light
Notification lights
FM Radio (Use Spirit FM, go to Settings -> Audio -> qsd8250)
All games should work
and more

Before you do anything maybe you should do a backup.

Download the ROM file from the topic on XDA.