1. Plug your USB cable into your computer and Sidekick
2. On the computer browse to the Sidekick drive folders

open "My Computer" then select the Sidekick's drive

3. You will see two folders listed, make a new folder here, name it "themes" (without the quotes)
4. Open that "Themes" folder
5. In that folder make another new folder with your new theme name.

this is the name you want to appear on the Sidekick backgrounds menu

6. Open Windows Notepad and paste the following text into it

string Name(en_US) themename
bitmap ring-background ring-background.png
bitmap ring-folder-background ring-folder-background.png

Or you can use a pre-generated template from here.

7. Save this .txt file to your newly named folder as "theme.txt"

there are more things that can be added and modified, this is a simple start. You can find an entire theme.txt template for every sidekick model here.

8. Save the picture you want as the main background in this folder. (ring-background)

make sure the name of the file should match the Notepad text file string and should be in PNG or JPG format

sizing for backgrounds is commonly listed as 240x138 pixels, otherwise image may appear stretched. An entire list of assets and sizes can be found here

9. Add the second picture you want for the sub category background. (ring-folder-background)

this is the same size as the main background file.

10. The picture file names must match the text file exactly, I sometimes save in jpg format but still leave the .png in the text line and the background will not load.
11. Close the files, unplug your USB cable from the device.
12. On your Sidekick select Menu/Settings/Backgrounds and your new theme name should be listed below the original four. This is the name you set as the folder and in the text file.
13. Select the new theme and it applies.

If you are unsure how to upload the theme to your sidekick 3 you can watch the video. Or you can click here to view photo examples of what it should look like here