simplest way is to reflash by using wotanserver.  free and simple, just click click and click.
but your phone data will be wipe completely. so backup your data first.

yup like new phone. wotanserver is a good tool but the website a bit serabut.

1. open wotanserver. create account and log in
2. select your phone
3. scroll down until u see "Tutorial: FREE Firmware Flashing & Debranding Sony Ericsson". click it.
4. or u just click http://www.wotanserver.com/en/page/tutoria...h-sony-ericsson
5. download 2 file there,  usb flash driver and wotan client.
6. install usb flash driver (double click usb flash driver.exe)
7. open wotan client.exe
8. wait till it download necessary data (15-30min, depend on your internet connection). meanwhile you can backup/sync/save/export your data while doing this. after that switch off your phone.
9. follow instruction.
10. on phone setting, choose enable advanced setting
11. select the correct model, firmware and CDA (look for malaysia CDA)
12. login with your account
13. wait till it flash your phone (another 15-30min)
14. viola, brand new phone. 
*and you may restore/sync/import back your data*

p/s: im not sure regarding data in sdcard, but i dont think it will wipe your data in sdcard, but to be safe, just make a copy to your computer.

wanna ask, when you flash your phone, did the root access gone?

coz he unlocked the bootloader previously. either u upgrade it via wotanserver or flashtool. u need the updated ROM before hand to flash it into ur unit then. no problem. it is just the beginning, bro~

yup. if you read back at first page where siuyi mention something about lock bootloader, it's the same method. and there are neo user report that it work.

so i guess you want to lock your bootloader to FOTA using SEUS isn't?

ah..i contacted the founder if the bootloader locking system, he told me the patchware for locking bootloader is only applicable for those who use his method for unlocking bootloaders (and his method is not the method i mentioned in page #1).

Don't flash back to older firmware, there's a problem with the 0% battery problem!

ax_86, mind to give details on what you have done?

So far the solution with the best success rate can be found here:

For Arc/Neo 0% battery problem: http://forum.xda-developers.com/showthread.php?t=1312398

glad to hear that too  feel like new phone right now eh? 
any lost of function after you reflash back using wotan server?
coz i reflash back using wotan server, but i can't use trackid anymore.