How can I extract the *.icns from the Get Info dialog? Previously, I've changed the icon of an application before by manually replacing the icon file .icns located in loremipsum.app/Contents/Resources/loremipsum.icns.

This time, I've downloaded some beautiful icons which are folders with the needed icon and not simple .icns files.

How can I get access of the the *.icns file?
You can mark it in the Get Info dialog, go Edit → Copy, switch to Preview, and select File → New from clipboard.