There is no upgrade directly to C6 from C4.  You'll want to find that magazine if you can.

Quote - So, if you have Carrara 4, make sure you upgrade now, as there won't be any upgrades to version 6 from anything older than Carrara 5.

You can read the whole post here: http://forum.daz3d.com/viewtopic.php?t=61943

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