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It's free. In iTunes click on your applications, "Check for updates" at the bottom, then the big "Download all Free updates" at the top.

I think devs might have a way to charge for updates which would normally only happen if a large portion of the app was changed I would think, similar to iLife '08 to iLife '09.
 
I think in the same way, but everytime when u update them, it will ask you to click "buy" to finish it, so that's y I doubt about it, :) thank you for answering!

:)
 
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