Where to write down the update infomation when submitting a update in app hub?

I just submitting a update version of my app in App Hub.

But what confused me a lot is that all the steps for updating is as same as when I submit a new app.

So I just don't know where to write down the update infomation.

I check the MSDN but found no answer with this, so,er,need help -_-

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