It is not possible to upgrade a Windows 8 installation that is using Full Disk Encryption through point releases. (E.g. Windows 8.0 to 8.1)
Attempting to perform a point upgrade on a Full Disk Encrypted system will result in the upgrade failing and rolling back the changes it attempts.
Therefore we strongly recommend you upgrade Windows 8 to the latest point release before commencing Full Disk Encryption. This is currently Windows 8.1.
If you are not sure which version of Windows 8 you are using, please click the following link to display the version of the machine you are browsing from. The page also includes instructions for identifying the operating system manually: Which Windows operating system am I running?
To initiate an upgrade to Windows 8.1, open the Store tile from the Start Screen, in Store, tap or click the 'Windows 8.1 update' link. For more information about the benefits of the new Windows edition and its installation please see this page: How to upgrade to Windows 8.1
If in the future should you need to update the machine to a new point release you will first need to decrypt the machine, perform the Windows upgrade and then re-apply the encryption.
Keywords: Windows, 8.0, 8.1, 8.2, UEFI, system, requirements, point, releases, full, disk, FDE, upgrade