Change firmware from cn to ww ?

Hello! I received my zenfone 2 Ze551ml yesterday and i figured that my firmware version is cn. As i live in Europe, should i change my firmware to ww? Is it safe and how to do it? (I found a tutorial on asus-zenfone.com and i don't know if i can trust it) The only problem i have so far is that some dialog boxes are in chinese.

My device is not rooted. Thanks for any help, sorry if bad english.