Debranding and unlock w850i

[Unkillable]

start setool, select phone model, click the add button and select the MAIN and FS file and click open, now click the "..." of MISC files and select the custpack. now click the flash button and do whatever setool tells you to do. you may need this too : Flash your phone and How to apply or remove patch using SETool 2 Lite - Top Sony Forums

Before i do this i need to do some backup or something like this?