Here’s the instructions for uploading a theme to the WDTV SMP (do not un-zip or change the file extension)
To install the theme, download the zip file to your PC, open your web browser (I don’t recommend using IE8 or 9, there have been issues), then type your SMP’s IP address to open the Web UI in your Web Browser.
Type in your password (the default is “admin”), click on the box next to “I accept” and then click on LOGIN, then click on “Appearance”, then click on “Browse” and navigate to where you saved the " LargeVideo3x3.zip" file.
Now click on “Open”. Click on “Submit”, then once the Web UI finishes uploading the theme.
On your SMP press “Setup” on your remote, select “Appearance”, then select “User Interface Themes”, select " LargeVideo3x3" then when prompted select “Apply theme”.
P.S. Uploading the theme should only take a few seconds … i would recommend using Firefox (or Chrome)
