How do I install Windows 8.1 Preview?
There are two ways to install Windows 8.1 Preview: through the Windows Store or through the ISO.
If you're running Windows 8 in one of the 13 languages that the preview is available in, we strongly recommend that you download the preview from theWindows Store. When you install from the Store, you can't create installation media but must download the preview directly from the Windows Store. If you're runningWindows RT, the only way you can update is through the Store. Updating through the Store will give you the same edition of Windows 8.1 Preview as the edition ofWindows 8 you're currently running. (For example, if you are updating from Windows 8 Pro, you will update to Windows 8.1 Pro Preview.) To see if you can update through the Store, see Download Windows 8.1 Preview.
If you're running Windows 8 and you want to install Windows 8.1 Preview using the ISO, it's important that you know where your Windows 8 product key is. When you update to the final edition of Windows 8.1 you'll need your Windows 8 product key to activate. To install Windows 8.1 Preview from within Windows 8, follow these steps:
Download the ISO (.iso) file.
Double-tap or double-click the ISO file.
Double-tap or double-click setup.exe and follow the steps
From Windows 8.1 Preview FAQ section.
Acc to FAQ I should install Via store to keep my files.