You'll need to use the Sony Flash Tool
if you want to update your unlocked bootloader device to the latest 314 firmware. But I believe that DooMKernel hasn't been updated to work with this 314 firmware (you will get bootloop if you update firmware and then flash the current DooMKernel).
So you either
(1) update to 314 and keep to stock kernel until DooMKernel is updated to work with 314 firmware
(2) wait for DooMKernel to be updated to support the 314 firmware before you update via Sony Flash Tool and then reflash DooMKernel.