Here is how to manually update your Nexus One (the original model, non-AT&T, non-rooted) to Froyo, Android 2.2.
- Download the update from here and save the zip file.
- Put the update onto your SD card and rename it update.zip (Note that if you’re using Windows and don’t have “show file extensions” turned on in the file explorer you won’t see a .zip. Just rename it to “update” (no quotes, of course) because it’s already a zipped file).
- With your Nexus One off, hold down the trackball and press the power button.
- You’ll be booted into a white screen with three Android robots on skateboards. Select “Bootloader.”
- On the next screen, select “Recovery.”
- Your phone will reboot, giving you a picture of the Android robot and an exclamation point inside a triangle.
- Now press the power button and volume up button at the same time. It could take a couple of tries.
- Now (using the trackball this time) choose “Apply sdcard:update.zip” and let things run their course, it will take several minutes.