Instructions
Connect an external hard drive such as an SD card or USB flash drive to your computer.
Double-click "Computer" to launch Windows Explorer. Locate your external drive's icon and double-click it to launch the disk window.
Right-click the disk window and select "New Folder" to create a new folder. Name the folder "PS3" (without quotes).
Double-click the "PS3" folder you just created, and then create a new folder. Name the new folder "THEME" (without quotes).
Drag themes from your computer to the "THEME" folder. If you're downloading a theme from a specific website, make sure you save it in the "THEME" folder.
Eject your external hard drive when you finish.
Connect your external drive to your PS3 gaming console. Select "Settings" on the main menu, then "Theme Settings," then select the theme you want to install and then select "Install."