I need to upgrade my 3GS on 3.1.3 BB 5.12.01 MC model to 4.1 ? Any clear answer,

[niu]

Sorry for posting a new but I have surfed the forum for how to do it but everything is confusing to me. so I wanted a single clear steps compatible with my IP like mentioned in the title. plus that it is locked on an operator which does not know. I unlocked it but seems to be not locked by ultra snow(i go to cydia & check the installed application & ultrasnow is not installed in my phone) since I bought the sim card which Sherif Hashim discovered to activate the phone & my brother did the upgrade&unlock to me from 3.1.2 tethered to 3.1.3 untethered.

Anyone could help me please. now I am following this link in this forum. could anyone confirm that it will work for me without any troubles regarding activating the phone nor unlocking my operator?

Link below : I am following & downloading the 4.1 IPSW official one & custom one. don't know why I have to download both.
100% solution to upgrade 3G 3GS 4G to 4.1 without upgrading the baseband (windows) - GSM-Forum

Please help me; because I am totally lost & get bored from 3.1.3 & want to experience the 4.x OS
I still have this sim card which activates the phone But I heard before that apple closed the exploit in it.

Hope to here your pro comments & instructions,thanks in advance.
running 7 32 bit
3GS on 3.1.3 BB 5.12.01 MC model

Please Anyone could help me? I downloaded everything & waiting for confirmed instructions. Please Moderators help me. My post have reached 68 read times but not 1 reply

I followed the steps from that link & then unlocked by ultrasnow & now my ip3gs is working fine untethered. Thanks for all who viewed.. But no body replied!
Regards,