Install with modgit:

$ cd /path/to/magento
$ modgit init
$ modgit clone admin-theme https://github.com/jreinke/magento-admin-theme.git

or download package manually:

• Download latest version here
• Logout from admin
• Unzip in Magento root folder
• Clear cache
• Login to admin

Switch theme from dropdown added in footer.

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