Simply follow the steps.

Step 1. Save the downloaded skins in your directory.

Step 2. Find AlbumOK skin directory.
(Ex : c:\program files\KoreaSorimachi\AlbumOK\)

Step 3. Paste downloaded skin into AlbumOK skin directory.

Step 4. Run AlbumOK. Click the right button of mouse,
        and then select [Change Info-> Change Skin] from menu.

※ Tip : You don't need Step 3, when you assign AlbumOK directory as a            Download directory.