Upgrade Zenfone Selfie to Marshmallow. [Through official update]

So Asus launched marshmallow update for Asus Zenfone selfie and brought the latest android update to us Zenfone selfie users.
I will skip the part where I tell what this upgrade brings and what is new in it. For that refer something else. I'm here to tell you how to upgrade. But yeah I can tell you one thing, this is an awesome update. It solves the battery issue because because of Android's new Doze mode.
Before, in the Lollipop,  if I charged my phone to 100% before going to sleep, I would wake in the morning and find that already 7-8% of my battery has already drained (In 6 hours of sleep). But now ever since I update my phone, I did some testing. I charged my phone to 5% before going to sleep. When I woke up, guess what.. It was still at 5%. Great right. And there are many other improvements.

Sorry for no screenshots, as I already updated my phone to Marshmallow and can not show the process again. I made sure that the process I write is detailed and easy so you wont need screenshots.

So you are here because they are not giving this update directly from software update from the phone itself. I don't know why they did that. But since they didn't gave FOTA (Firmware other the Air) on the phone but on website, it confuses how to do it.
I tried installing it though adb, the method which everyone finds on the internet. But it didn't worked. It showed "Cannot read update.zip" error. So if you are stuck like that, follow this procedure and it will work. 
If you don't know what the above line means, that is alright.. just follow me.

Before you begin:
1.Make sure you update you phone to WW_1.15.40.1582. For doing that, you just need to open software update in settings and check for updates. 

For those who don't know what the above number is, it is the version of software provided by the Asus for the Selfie phone. It you think that why this number is used to define the software version and why not Android version 5.0 or 5.1. It is because, every Company like Asus need to modify the android package so that their android is a bit different than the others. So they take the android provided by the Google (Owner of android) and modify it up to their needs. Every android ROM need to be modify for every phone. One ROM cannot run on any other device for which it is not made.

Continuing on our topic, If you want to check that you are at correct version, 
Go to Settings>>About>>Software Information. Under Build Number, you will find your numbers.
Make sure it is WW_1.15.40.1582.

2. Another thing you want to make sure that you have 2 to 3 GB free space on your phone memory. You can use and external SD card also.

3.The marshmallow update doesn't supports App2SD, so all the apps that are in your SD card will be removed. SO before you begin, make sure to move all your apps from SD card to your phone. (Blog update 21-Aug-2016)

4.Also backup all you data in case something goes wrong (Probably it won't).

Now, when you have done and checked all the above, Follow these:

 1.
So First,
You need to download the marshmallow upgrade file from the Asus website.
Here is the direct link:
Download Zenfone Selfie Marshmallow Direct Link.

If the above link doesn't works, you can click this link to open Asus website
http://www.asus.com/in/Phone/ZenFone_Selfie_ZD551KL/HelpDesk_Download
Go to drivers and tools, and select OS "Android"
Scroll down to find the upgrade file. It is named Version WW_21.40.0.169. 
Download that 1.63GB zip file. Doesn't matter where you download it, on PC or phone.

 2.
Once you have downloaded the file, make sure your phone is charged at least 40-50% as it takes time to upgrade. You don't want to switch off the phone while it is being upgraded as it may Brick your phone. (Which by the way means that your phone becomes useless and only people at service center can repair your phone.)

 3.
Now copy the zip while as it is "without extracting" to your phone.
Not anywhere, In ASUS folder of your phone memory.
(If it doesn't contains ASUS folder, which is unlikely, create it.)
If you are using external SD card, make ASUS folder in the SD card and copy it to that folder.
[Blog Update 27/08: Even if you copy the zip to phone memory, it will show you the update. Thankyou ANIKESH008 for confirming this.]
If you don't copy it to correct folder, it will not show upgrade option. There is no danger if you copy it to wrong location. If you have question, please write it in comments.

 4.
Now once you copied the file, switch off you phone and start it again. Once the phone has booted up, completely, it will show "Update Found" in notification bar. Just click it, and it will start the update.
Follow any onscreen instructions and let it do its work. It will take some time to update so make sure your phone is charged. You can plug into the charger also just to be on safe side.

And done. Your phone is now updated to Latest android. 
Have any question, please feel free to write in comments.