Hello toka
After further research into your issue I can explain how you can get your computer upgraded to Windows 8.
The Notebook came with Windows 7 installed and is not one of the operating systems on the driver page as I suspect whoever sold it to you removed Ubuntu and put a copy of Windows 7 instead. The system cannot automatically update itself to Windows 8 it has to be purchased and installed manually. I would recommend that you go to a local electronics store to see if you can purchase and then install the Windows 8 operating system. Once you have purchased a copy of Windows 8 and installed it you can download and install the Windows 8 drivers from the HP Pavilion Ultrabook 14-b011tx Drivers page.
I am sorry for the confusion in regards to getting your HP Pavilion 14 Ultrabook to Windows 8. Thank you for posting your issue on the HP Forums. Have a great day!