Update: I’m updating this post after successful upgrade of Windows 8 enterprise to Windows 8.1 enterprise. If you are using Windows 8 enterprise version at home, you would be in slight trouble now, because you can’t upgrade it to Windows 8.1 by Windows store or control panel or even by the publicly available Windows 8.1 enterprise ISO from Microsoft site. Windows 8 enterprise can be upgraded only by the medium you download from Volume Licensing Service Center (VLSC). Mostly only EA business customers of Microsoft have access for VLSC.
It’s very rare and special case that someone will have Windows 8 enterprise version on home computers.
Note: If you think you are smart enough ( like me) to upgrade existing Win 8 enterprise with 8.1 ISO which is available as 90 days trials, sorry that will not work. I tried this method on a virtual machine, it installed as a new Operating System, and even I could not used the old OS, because It moved the all of my files and system files to Windows.old folder.
Microsoft clearly says the reason as below why normal update is not possible by Windows store.
How to Update Windows 8 Enterprise to Windows 8.1 Enterprise
1) Download the ISO from Volume Licensing Service Center (VLSC). Make sure to download correct 32 bit or 64 bit matching your existing OS version.
2) Create a DVD or USB (bootable).
4) Next screen is to download the latest updates from Microsoft site while installing.
5) This step is very important. Obviously we do not need to lose any existing data, programs and Windows settings. So, select the first option.
As mentioned earlier, if you try this update with normal Windows 8.1 enterprise ISO which is available for public, you will get only ‘Nothing’ option, which will be considered as a fresh installation.
6) Installation will start smoothly.
7) Once installation has completed, you will go through customizing Windows ( I like to use express settings option).
8.) Good thing, it did not ask me to login or create online Microsoft account. It picked up my old Windows 8 local user account.
9) For some strange reasons, even after I entered my local user account credential, it showed below error related to setting up online Microsoft account. I did not bother as I do not want to login with online user account which will create another new user profile.
10) After settings up and configuring apps and other settings, you will get the upgraded Windows 8.1 enterprise desktop. It will keep your files, settings and same profile.
So, updating Windows 8 enterprise to Windows 8.1 enterprise is very easy and straight forward. But, this can be done only by the medium you download from Volume Licensing Service Center (VLSC).
If you are using Windows 8 enterprise in business organization, then your IT department may deploy the update across the organization by using Microsoft Deployment Toolkit (MDT) 2013 or System Center 2012 R2 Configuration Manager
Download Windows 8.1 Enterprise
If you like to try Windows 8.1 enterprise version separately, you can download a 90 days trial version from Microsoft site here.
Sysprobs already published a guide about how to install Windows 8.1 on VirtualBox as virtual machine.