While there have been ways on how to get Amber update on the Nokia Lumia 920 but those methods apply to only to the International unlocked version. Now, snickler has come with a method on how to download Amber update on the Nokia Lumia 920 on AT&T network. This method is completely safe. Just make sure you follow the steps carefully.
Steps: via xda
* DONT PLUG IN YOUR PHONE YET TO THE COMPUTER.
* Extract/Install Nokia Care Suite. Open Care Suite when it’s done installing and just put it to the side
* Install WperHelper. It’s all in chinese, but the buttons should be easy to navigate through
* Download the last group of files for the pre-portico ROM if you haven’t done so already.
* Go to the Run menu on your system and go to "C:\programdata\nokia\Packages\Products". Create a new folder named "RM-820". If you already have files in here from a previous ROM installation, move them somewhere else. The group of files you downloaded for the Pre-Portico ROM will need to be moved inside of this folder.
* Rename the pre-portico files removing the checksum from beginning of the file name.
Here’s what you should have as files
* RM820_1232.2109.1242.1002_RETAIL_nam_canada_200_02 _100347_prd_signed.ffu
* CustomerNvi_31019d17537fb461136cdf3481825681_12421 _100343_8410.nvi
* RM820_059R2L8_1232.2109.1242.1002_039_signature.bi n
* Go back to NCS and double click on the Product Support Tool. If you don’t see the little menu with the choices of apps to install, go to "C:\Program Files (x86)\Nokia\Nokia Care Suite\Product Support Tool For Store 5.0" and click on ProductSupportToolForStore.exe (Make sure the icon is an arrow. We don’t need to open the .MANIFEST file).
* When the Sign in popup comes on the screen. click Work offline.
Click File -> Open Product and type in RM-820 in the filter then press Open
* At the bottom left panel, click on Programming -> Recovery.
* In the Properties listing, you should see 059R2L8 RM-820_Rogers_Canada_VAR240202_V2_Yellow 1232.2109.1242.1002
* Click on that line that shows the data that I listed above then click the Start button.
* Plug in your phone to the USB now, hold the Vol-Down + Power buttons until the phone restarts and you hear a vibration.
* When you hear the vibration, press Retry.
* You should see a little menu saying that the Product Code doesn’t match, press Okay to continue.
* Let it flash.
* After the phone has flashed, set it up, but don’t login to your Microsoft account yet (It’s pointless at this point). Configure Wi-Fi though.
* Go to Settings -> Phone update and check for updates. The first round of updates will put you on to Portico.
* After these updates go through (It will take forever for it to finish Preparing to Install), you’ll have to check for updates two more times in order to install Nokia Updates.
* After these two extra updates, your phone will be up to date.
* Now comes the fun part. Open up the WperHelper that you installed earlier.
* On the Top group of text links(The bigger text), chose the second one from the left. It should bring up a screen with 4 drop downs.
* From left to right, choose the following as values: Nokia, Lumia 920, RM-820, 3047.0000.1326.2001.
* Click on the 059R2L5 button that is located under the first dropdown. At the bottom right part of the screen, you’ll see a download icon (downward facing arrow with a line underneath of it). Click it.
* This will start to download the ROM. When complete, Click on the Top group of text links, click on the third one then click on the second smaller text link underneath of it.
* You should see bbs.wper.com_059R2L5.7z. Click on it then click the lightning bolt on the bottom left corner. This will extract the FFU package.
* After it’s complete, you’ll see a new screen with a picture of a Windows phone and a bunch of Chinese text (I wish I had a translation). At this point you’ll want to click the button that is listed directly under ( Step ).
* This will automatically begin the ROM updating process. You’ll be able to see a little log running at the bottom of the screen on whether the Flashing is working or not.
* The place where the Windows Phone is showing will display the actual progress of flashing as it appears on your phone. You should be seeing the red screen with the progress bar on your windows phone by now. If this happens for you, then you’re on your way to having the Amber Update.
A few things to note
After fully flashed, it’ll bring you back to the typical phone set up screen. After you get to the main homescreen, wait a minute or so because it will require a reboot. After you bring the phone back up, go to Settings -> Access Point and choose AT&T – LTE 2 – Lumia. This will set up the MMS and Data settings correctly.
To get internet sharing working on AT&T network, follow this thread on windows phone help site.