Your new blue-black theme should appear under the "Installed Themes" or "Visual Styles" section. Click it to apply.
By default, Windows 7 does not allow third-party (non-Microsoft) themes. To enable them, you must use a "Universal Theme Patcher." theme-windows-7-blue-black-kuyhaa
After downloading, you will typically find a .theme file and a corresponding folder of the same name. Your new blue-black theme should appear under the