Note: The contents are taken from [How-To] Manually Update Nexus One to Android 2.2 FRF83 (6/23/2010) - Android Forums
Here's a thorough run through of everything that FroYo brings:
Android 2.2 Froyo: everything you ever wanted to know -- Engadget
Unfortunately, for now, this method is only for stock users of the "T-Mobile" version of the N1. If you are rooted and have an unlocked bootloader, I have special instructions below.
There're are a few ways to end up at FRF83. If you're on 2.1, go to FRF50, then straight to FRF83.
If you've already flashed 50, then 72, take the file from 72 to 83.
Manual Update Instructions
1. Download file from the following link(s):
From 2.1 to FRF50
From FRF50 to FRF72
From FRF50 to FRF83
From FRF72 to FRF83
If you don't know your build number, go to settings, about phone
2. Rename the file to update.zip
3. 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.
4. Copy the update.zip file onto the root of your microSD card (that means not in any folders)
5. With your Nexus One off, hold down the trackball and press the power button.
6. You'll be booted into a white screen with three Android robots on skateboards. Select "Bootloader."
7. On the next screen, select "Recovery."
8. Your phone will reboot, giving you a picture of the Android robot and an exclamation point inside a triangle.
9. Now press the power button and volume up button at the same time. It could take a couple of tries.
10. Now (using the trackball this time) choose "Apply sdcard:update.zip" and let things run their course.
Taken (and modified) from the update-1 instructions on:
How to manually update your Nexus One | Android Central
Special thanks to:
cedriCz_ : For the link to the file on Google's servers
inspiron41 : For the instructions
Androidcentral: For the instructions
Cyanogen: For rooting 2.2!!
Special Instructions for AT&T N1 owners
This file is an update from ERE27 to Froyo, which means that if you want to use it, you will manually have to install ERE27 first, then run this file to get your frozen dessert. This requires you to unlock your bootloader!
Special Instructions for Rooted Users - *This may now be outdated.
You can get this update, which has been prerooted for you by Paul @ MoDaCo. You know the drill on how to install these ROMs:
FRF50 (Froyo) pre-rooted update zip - Android @ MoDaCo
UPDATE: Froyo has been rooted! - *This may now be outdated.
Quick rooter for stock FroYo systems - xda-developers
Install this file the same way you installed the 2.2 update file.
Direct link to the file: