Solution 1:

If anyone is interested: Ctrl+Alt+D combo helped me.

Solution 2:

In Visual Studio 2013 running SSDTBI for VS 2013 the option has moved to the "View" menu, and confusingly it only shows if an actual report has focus. So click somewhere in your report, and then click "View"

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Or as stated by others Ctrl+Alt+d still works, though only if you have a report focussed.