Instructions
Plug an external drive such as a flash drive or SD card into your computer.
Double-click "Computer" on the desktop or the Start menu to display Windows Explorer. Locate your external drive's icon and double-click it. A new window launches.
Right-click any part of the window, select "New," and then click "Folder" to create a new folder. Name the folder "PS3" (without quotes). Double-click the new folder to open it.
Create a new folder and name it "Theme." Double-click the new folder to open it.
Drag a theme from your computer to the "Theme" folder. If you're downloading a theme, go to the appropriate website and download it to your computer. Drag the downloaded theme into the "Theme" folder.
Right-click the new theme you added to the "Theme" folder and click "Rename." Rename the file whatever you wish and keep the P3T file extension at the end. For example, if you want to name your theme "Smile," you will type "smile.P3T" (without quotes). Close the "Theme" folder when you finish, and then eject your external drive.
Connect your external drive to your PS3. Turn on your TV and your gaming console to view the XMB menu.
Select "Settings," then "Theme Settings," then select the theme you added to your external drive, and then select "Install."