Microsoft official guide: Win8.1 preview upgrade /installation method

        The Win8.1 preview upgrade/download has been released. How can different user groups experience the Windows 8.1 preview? Take a look at Microsoft's official guidance:
First, can any user try the Win8.1 preview version?
We strongly recommend that only experienced computer users download Windows 8.1 Preview or Windows RT 8.1 PrevIEw. Before downloading this preview release, you should weigh the pros and cons of installing software that is still under development. If you install this preview version, you can try a lot of new features, but you will also get an error that you won't encounter with a released version of Windows.
Warning:
If you are running Windows RT, you will not be able to restore Windows RT after installing Windows RT 8.1 PrevIEw. You will be able to upgrade to the final version of Windows RT 8.1.

Second, how to install Win8.1 preview version?
There are two ways to install Windows 8.1 PrevIEw: via the Windows Store or via ISO.
1. If you are running a Windows 8 version of the language that is one of the 13 languages ​​available in this preview, we strongly recommend that you download this preview from the Windows Store. When you install from the app store, you can't create the installation media, you must download the preview version directly from the Windows Store. If you're running Windows RT, there's only one way to update it, either through the app store. To find out if you can update through the app store, see Download Windows 8.1 PrevIEw.
Warning:
• If you are running Windows 8, and you are not using any of the 13 language versions of this preview, you will need to install using ISO.
• If you are running Windows 8 Enterprise, you will need to install this preview version using ISO.
2, if you are running Windows 8, and you want to use the ISO to install Windows 8.1 Preview, you must know where your Windows 8 product key is. When you update to the final version of Windows 8.1, you need to use the Windows 8 product key for activation. To install Windows 8.1 PrevIEw from Windows 8, perform the following steps:
1 Download the ISO (.iso) file.
2 Double-click the ISO file.
3 Double-click setup.exe and follow the steps.
If you are running Windows XP, Windows Vista or Windows 7, you can download the ISO image and use it to create a bootable DVD or USB drive for installing Windows 8.1 PrevIEw.
Notes
• If you need to update the firmware or drivers during the installation process, you should install all required updates in Windows Update.
• If you need to free up disk space during the installation process, consider copying the file to a USB stick or uninstalling an application that takes up a lot of space.
• If you start getting Windows 8.1 PrevIEw but decide to stop, be sure to uninstall the associated Windows Update. Open the Control Panel and search for the installed updates. Find the Microsoft Windows category and then uninstall KB2849636.