Android: How to upgrade your Nexus One from Android 2.1 to 2.2?

To manually install Android 2.2 on the Nexus One, perform the following steps:

1. Download the official Android 2.2 firmware for the Nexus One.
2. Copy the file to your microSD card and name it update.zip (newb warning: not update.zip.zip)
3. Power off your phone.
4. Hold down the VOLUME DOWN button and power it back on.
5. The phone will now search for files like PB00IMG.zip, etc. This is normal. Scroll down to recovery and press the POWER button.
6. When you see the “/!\” symbol, press the POWER button and the Volume Up button at the same time. You should be presented with a menu and one of the options should be “Apply sdcard:update.zip”.
7. Use the trackball to navigate to “apply sdcard:update.zip” and select it.
8. When you see “Install from sdcard complete”, select “reboot system now”.

Enjoy and once you’ve had a chance to play for awhile let us know what you think.

The resources:
- Upgrade from Android 2.1 (ERE27) to FRF50.
- Upgrade from FRF50 to FRF83.
- Upgrade from FRF72 to FRF83.
- Upgrade from ERD79 to ERE27. (~16MB),
22607-ERD79-update-nexusone-stock-signed-boot-img. (~2MB)
- Update for ERE27. (~65MB)

(Referred from: AndroidAndMe, Links from the Net)