4 steps upgrade firmware for your Amazon Kindle 3rd

1.Go to this link http://www.amazon.com/gp/help/customer/display.html/ref=hp_navbox_top_kindlelgi?nodeId=200529700
& download Kindle 3G (Free 3G + Wi-Fi) - U.S. and Canadian Customers*:  Download 3.1 (Early Preview Release)
Your serial number will start with "B006" (My Kindle bought for US Amazon & chose this version)

if your Kindle is wifi, please select this 

Kindle Wi-Fi: Download 3.1 (Early Preview Release) 

Your serial number will start with "B008"

2.To connect you Kindle by USB cable , then open the Kindle storage disk and drag & drop you download file "Update_kindle_3.1_B006.bin" to the disk.

(you will see a lot folder ,just put on the directory & no into any folder)

3.Eject the Kindle to disconnect safely Kindle from your computer.

4.press "Menu" button and select "Settings" => press "Menu" again and select"Update Your Kindle"

It will take about 5 to 10 minutes. Just take a rest and do not touch your Kindle(It will power on and shut down automatically more times)  

Check your version:

press "Menu" button and select "Settings"

If you see "Version:Kindle 3.1" on the right down

Congratulation

It's easy by 4 steps to update your Kindle firmware.