How change cyanogen mod to stock firmware please?

Hello

can you tell me step by step how can I flash stock firmware on cyanogen firmware?

I tried flash with flashtool and I see this:

Code:

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21/054/2015 22:54:00 - INFO  - Selected Bundle for Sony Xperia SP (C5303). FW release : 12.1.A.0.266. Customization : CE
21/054/2015 22:54:00 - INFO  - Preparing files for flashing
21/055/2015 22:55:56 - INFO  - Please connect your device into flashmode.
21/056/2015 22:56:26 - INFO  - Device connected in flash mode
21/056/2015 22:56:26 - INFO  - Opening device for R/W
21/056/2015 22:56:26 - INFO  - Reading device information
21/056/2015 22:56:26 - INFO  - Phone ready for flashmode operations.
21/056/2015 22:56:26 - INFO  - Opening TA partition 2
21/056/2015 22:56:26 - INFO  - Current device : Unknown: Jan 19 2014/22:13:32 - YT910A3L5T - Unknown: Jan 19 2014/22:13:32 - Unknown: Jan 19 2014/22:13:32 - Unknown: Jan 19 2014/22:13:32
21/056/2015 22:56:26 - INFO  - Closing TA partition
21/056/2015 22:56:26 - INFO  - Start Flashing
21/056/2015 22:56:26 - INFO  - Processing loader.sin
21/056/2015 22:56:26 - INFO  -    Checking header
21/056/2015 22:56:26 - INFO  -    Flashing data
21/056/2015 22:56:31 - INFO  - Loader : S1_Root_7054 - Version : R5G006 / Boot version : R11B023 / Bootloader status : ROOTABLE
21/056/2015 22:56:31 - INFO  - Max packet size set to 64K
21/056/2015 22:56:32 - INFO  - Making a TA backup
21/056/2015 22:56:32 - INFO  - Opening TA partition 1
21/056/2015 22:56:32 - INFO  - Start Dumping TA partition 1
21/056/2015 22:56:37 - INFO  - Finished Dumping TA partition 1
21/056/2015 22:56:38 - INFO  - TA partition 1 saved to C:\Users\jirka\.flashTool\registeredDevices\YT910A3L5T\s1ta15-09-21_10-56-32.ta
21/056/2015 22:56:38 - INFO  - Closing TA partition
21/056/2015 22:56:38 - INFO  - Opening TA partition 2
21/056/2015 22:56:38 - INFO  - Start Dumping TA partition 2
21/056/2015 22:56:39 - INFO  - Finished Dumping TA partition 2
21/056/2015 22:56:39 - INFO  - TA partition 2 saved to C:\Users\jirka\.flashTool\registeredDevices\YT910A3L5T\s1ta15-09-21_10-56-32.ta
21/056/2015 22:56:39 - INFO  - Closing TA partition
21/056/2015 22:56:39 - INFO  - Ending flash session
21/056/2015 22:56:39 - ERROR -
21/056/2015 22:56:39 - ERROR - Error flashing. Aborted
21/056/2015 22:56:39 - INFO  - Device connected in flash mode
21/056/2015 22:56:41 - INFO  - Device disconnected

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I tried lock bootloader, still not work, only phone did not start up, so I again unlock bootloader with code what flashtool readed from it.

I have no experiences with this, do I need anything else except lock bootloader to stock firmware work? Like is needed reflash some boot.img etc?

thank you