[Sony Xperia M] paper13579:
PART 1:

If you have already updated to 4.3 then read this, if u havent, skip to the next part:

1. Go to settings

2. About phone

3. Go to bottom an click the build number ten times. This enables you as a developer.

4. Back into settings and click developer options.

5. Enable usb debugging.

6. Download this ftf: https://docs.google.com/file/d/0B_d8uWGbkaetc2hZbmNtdWZTYmM/edit?pli=1

7. Download flashtool from here: http://www.flashtool.net/download.php

8. Install flashtool

9. Open the folder where you installed flashtool.

10. Put the .Ftf file you downloaded earlier in the firmware folder of flashtool

11. Go back and run flashtool

12. Click the lighting icon

13. Click flashmode then ok

14. From the list pick the .FTF file you download earlier. And at the bottom click flash.

15. Wait a while, while it prepares the files

16. When a new window with a phone shows up, get your usb cable.

17. Attach the fat end into the computer.

18. Turn off your phone.

19. Press and hold the volume down button, while inserting the small end of the usb cable into your phone.

20. Let it flash the firmware.

21. When finished, remove the usb cable from your phone and turn it on.

22. Now you are on android 4.2.2

PART 2:

If you followed part 1 or if you are already on android 4.2.2 then keep following part 2. This part is not optional:

23. Follow steps 1-5 again from part 1

24. Download the software from the website: http://www.cydiaimpactor.com

25. Attach your phone to the computer, while it is on

26. Run cydia impactor.

27. When finished, remove the usb cable.

28. Go to Google playstore and download supersu.

29. Run it and let it update the su binary.

30. Now you are half rooted on 4.2.2

31. Download busybox by stericsson from the google playstore.

32. Install busybox.

33. Download this software: http://www.2shared.com/file/e9sDTGJk/rootfixer.html?

34. Extract it

35. Run supersu.bat

36. Follow the on screen instructions.

37. Now you have full rooted 4.3

PART 3:

This is where we flash the 4.3 rooted firmware. Everyone follows part 3, it is not optional:

38. Download this FTF: https://docs.google.com/file/d/0BzSvKAuDHQkAaXpBc25zc1oxM0U/preview?pli=1

39. Optional: download winrar or 7zip.

40. Open the ftf using winrar.

41. Drag the system.sin file in the ftf to your desktop.

42. Follow steps 7-8 in part 1 if you haven't already installed flashtool.

43. Run flashtool.

44. Press on the tools tab at the top

45. Press sin editor

46. Browse for the system.sin file you extracted earlier from the ftf

47. Press extract data

48. Now you will get a system.ext4 file

49. Download the nickiroot 1.0.1 (it's what i used) software from the OP (main thread)

50. Extract it

51. Place the system.ext4 file in the same folder as the root.bat file from the nickiroot software.

52. Run root.bat

53. Attach your phone to the computer while it is on.

54. Let it work, this will take around 25 minutes, be patient.

55. Remove the usb cable from your phone.

56. Remove the back cover of your phone

57. Remove battery.

58. Wait a minute

59. Insert battery.

60. Put cover back on

61. DON'T TURN ON THE PHONE. IF YOU DO, START AGAIN FROM STEP 19 PART 1

62. Place the FTF you downloaded in part 3 in the firmware folder of the flashtool folders

63. Run flashtool

64. Click the lighting icon

65. Click flashmode then ok

66. Click on the FTF you just placed in the firmware folder from the list. DON'T PRESS FLASH YET. IF YOU DID, START AGAIN FROM STEP 1 PART 1.

67. From the list where it says exclude at the top, tick the box of system.sin

68. Now, press flash.

69. Follow steps 15-21 of part 1

70. When you turn on your phone look for the supersu app and open it.

71. If it tells you that you are not rooted then start again from step 1 part 1, you must have made a mistake somewhere. If it says nothing and just shows you the log, then you are fully rooted on android 4.3. VICTORY

Damn that was one hefty explanation. If you don't understand something, then FML.