How to upgrade from Windows 8 to Windows 8.1 offline using an ISO

The Microsoft method of upgrading Windows 8 to Windows 8.1 is to use the Windows Store to download the update, and upgrade on the fly. However it sucks if you have a lot of PCs to upgrade, or just wish to redo the process without needing to download the huge amount of data (around 3.5 GB) over and over again.

Thankfully, there is a technique of getting the Windows 8.1 ISO from Microsoft and using it to upgrade your Windows 8 PC. The first step is to download the official Windows 8.1 ISO. Officially, the Windows 8.1 ISO can be downloaded only by customers who’ve purchased a Windows 8.1 key. Those who’ve purchased a Windows 8 key cannot use the key to download the Windows 8.1 ISO. However there is a workaround.

To download the Windows 8.1 ISO, follow the following steps:

1. Download the Windows 8 Installer and run it.
2. Enter your product key and proceed until it starts downloading. Now exit the Installer.
3. Download the Windows 8.1 Installer and run it.
4. It will start downloading Windows 8.1 installation files.

If you directly try to download Windows 8.1 installer, it will ask for a Windows 8.1 key and reject your Windows 8 key.

Once you have the Windows 8.1 setup downloaded fully, elect to write the setup to a USB disk.

Now you need to modify a few things on the USB.

First, you need to make sure that it doesnt ask for a license key at the start of installation, and instead asks for installation key at the end. It is because if it asks for a key at the beginning, it rejects a Windows 8 key and requires a Windows 8.1 key. If it asks for a key after installation, it accepts your Windows 8 key. So you need to do the following:

In the directory named ‘sources’ create a text file named ei.cfg with the following contents:

[EditionID]
Professional
[Channel]
Retail
[VL]
0

Now, edit the file cversion.ini and change the following:

MinClient=9458.0
MinServer=9458.0

to:

MinClient=9431.0
MinServer=9431.0

This will allow Setup to proceed without an initial reboot even on Windows 8.

Now, run the setup. After installation, on reboot, you will be asked for a license key. Enter your Windows 8 key, and Windows will be activated! Welcome to Windows 8.1!