Many people have shared the update on zipped files.
I wanted to know, if I download the update in zip file and transfer it to my mobile, how can i manually install the update myself?
I have found the steps to update the froyo:
1. Download the Android 2.2 firmware for the Desire – here is the link to download
2. Rename the file update.zip and copy it to your microSD card via USB. [Note: make sure the file is named update.zip and not update.zip.zip.]
3. Power down your Desire
4. Hold down the “Volume Down” button as you power the phone back on.
5. A screen should appear showing your phone’s system searching for various files. Scroll down to “recovery” and press the “Power” button.
6. When you see the triangle with an exclamation point symbol, press the “Power” and “Volume Up” buttons at the same time.
7. From the menu that appears, select “Apply sdcard:update.zip.”
8. When the screen displays “Install from sdcard complete” select “reboot system now” and wait for the phone to power back up.