Default [Q] original software I9100XXMS2

I have bought one S2 from Amazon Germany and come with CyanogenMod.
Unfortunately, from time to time phone loose network signal and call close.
I need your help to restore original software. And, cause I had another S2, I saw have android version 4.1.2, I910XXMS2, version number JZO54K.I9100XWLSS.
I'm not specialist on this and I appreciate detailed informations, not to lock/block something.
Phone don't have any information inside, so I don't have to be worry I'll lose something.