So if you own a Nexus One mobile phone and don’t have the Android 2.3.4 update, then you may download it here. Then simply follow these steps to perform the update.
1. First rename the downloaded file to update.zip.
2. Copy this file to your microSD card that fits into your phone.
3. When you still have your Nexus One phone switched off, simply press the trackball and then press the power button.
4. When the white screen boots, with three Android robots on skateboards on the screen, select “Bootloader” from the available options.
5. When the next screen appears, simply select “Recovery”.
6. After the device reboots, press both the volume up button and the power button together.
7. Once you are through with that, choose the option “Apply sdcard:update.zip” to complete the update.