HTC released first firmware for HTC Desire 1.15.405.4. At this point of time there are no details available for general public as to what exactly are the new features or what it fixes.

According to HTC website

"In our commitment to providing you with the best user experience, we are pushing out a new firmware update to your phone"

Installation Process:

Users will receive notification of this update when it is made available.

To upgrade the firmware all you have to do is press OK button and select WiFi or GPRS/3G.

To check & confirm new firmware go to MENU> Settings> About Phone> Software information> Software number)

Note: Users are recommended to find a free Wi-Fi hotspot or an unlimited data plan to apply this update. HTC Desire's New firmware version is 1.15.405.4.

Source: HTC