Hello,

I have got a preinstalled Windows 8 on my pc. Is it possible to upgrade it to windows 8.1 offline?

AW

You can only update offline if you download the Image and run it locally.  It will however need to be validated online at some point.

Hi,

You can easily upgrade your Windows 8.1 system by Windows Store, this is online

http://windows.microsoft.com/en-in/windows-8/update-from-windows-8-tutorial

If you want offline installer, as  Zigzag mentioned, you need a image and run it locally, I recommend you refer to this guide to perform this, you need a valid license key

http://blogs.technet.com/b/canitpro/archive/2014/03/19/windows-8-1-tips-how-to-download-the-windows-8-1-pro-iso.aspx

Regards.