i need some help for update s2 to 4.1.2

hello everyone
straight away i am sorry for my poor English

my problem is that i wont to update my Samsung galaxy s2 from 4.0.3 to 4.1.2
but i am noob i red a lot in xda developers also i red a lot in a Google but i don't sure where to start because as i know to update too 4.1.2 you need to have original unlocked s2 and my one is from UK on the carrier 3 and i unlocked it by nspro

and for a s2 on carrier 3 the 4.1.2 has not been released yet

so my question is can i re-flash my s2 with 4.1.2 even though i am on carrier 3

and if i can can someone redirect me where i can download debranded rom
for my S2

because i red an information in Android 4.1.2 Jelly Bean Official Update Available For Samsung Galaxy S2 (GT-I9100): How To Install It Manually [Tutorial]
and i download I9100XWLS8_I9100FOPLS3_FOP but i am not sure if this good for me

my phone details
PDA: I9100XWLP7
CSC: I9100H3GLP3
PHONE: I9100NELP3
Version: Android 4.0.3 Ice ***** Sandwich
Kernel version: 3.0.15-I9100XWLP7-CL340913dpi@DELL134 #3
Build number: IML74K.XWLP7
Carrier: UK 3

BY THE WAY MY PHONE IS ROOTED but i newer tried to write another rom

many thanks
gugutm