If you get an error "The update is not applicable to your computer", follow these steps.
1. Add the English US language:
2. Set the OS Installation and default to English US in the registry:
3. Check if the language is set to English using DISM:
4. Install the Security Update KB2849636
5. Restart the computer, open the Store and click on the Windows 8.1 download.
6. You should see the Installs screen and (slowly) moving progress bar.
7. Enjoy the Windows 8.1 preview
URL link reference to the kb2849636 is wrong.
Search for "Windows8-RT-KB2849636-arm.msu" instead and everything would work fine.