after yum upgrade f17 to f18: still on f17 ?

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http://forums.fedoraforum.org – Hi, I did a yum upgrade from f17 to f18, and despite no apparent problems, I still have f17 in the grub menu, no f18. Also, uname -a show I'm on f17 instead of f18. Any idea what I forgot or has gone wrong ? Thanks (HowTos)