In previous versions of Windows from Windows Vista up to 8.1 upgrading to the Enterprise SKU of the product required you to actually have the install media for this edition.
In the Windows 10 Technical Preview, Enterprise is still offered as separate install media, however what’s different this time around is that you can now simply upgrade from the Pro SKU to Enterprise directly from within the OS.
This option seems to have been available since 990x Builds such as 9901 (At least this is when I first noticed it) and is still present in Build 9926, all you need is the product key.
1. Firstly you will need to obtain the Windows 10 Enterprise Technical Preview Product Key. That’s easy, here it is: PBHCJ-Q2NYD-2PX34-T2TD6-233PK
2. Go to Control Panel and select “Add features to Windows 10 Technical Preview”
3. Select the option “I already have a product key” and enter the above key
4. Accept the license terms and add the feature
5. The feature will be added and the machine should automatically reboot twice during the process.
P.S For those of you who would also like the Enterprise ISO for Build 9226 you can download it from the direct links below.