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I’ve found some “Design"-related option in: “System” -> “Configuration” -> “General” -> “Design” -> “Package” -> “Current package name”
and tried to change the package name to “magento_classic_theme_free” the name of the package I’ve found here http://www.magentocommerce.com/extension/928/magento-classic-theme and successfully installed it.
But anyway it says that “package with this name does not exist and cannot be set.”
Also I want to mention that there is no any information on how to change skin as administrator using some controls in Admin End.
I’ve searched the Wiki and User Groups and all other Documentation and Tutorials available on this site.
You’re in the right area, but putting in the wrong setting. The theme name is not the name of the package, but instead the name of the directory.
I’m not sure what classic is called, but use your file manager to go to /skin/frontend/default/ and you should see all the available themes you have installed. My guess is the directory will be named “classic” or something.