S2 has already got official jelly bean rom from Samsung. So most likely you can upgrade it directly from Samsung with kies. If that failed, and the phone is international version you don't need to root it to Flash jellybean. All you need is odin and official jelly bean rom from Samsung which are widely available in sammobile. There's are also many third-party rom available like CM rom.
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Thanks. I watched the video and it does look reasonably simple. If I should want/need to revert to OOTB, does the zip that CWMRecovery created enable that? Meaning is it reverted to exactly what it was before the flash?
BTW sorry for the delayed response. I never got an email telling there had been a reply.