Things You'll Need
Instructions
Remove the DSTT card from the Nintendo console.
Remove the microSD card from the DSTT card.
Insert the microSD card into the microSD card reader. Windows will immediately detect it as an external storage device and assign a drive letter to it.
Open the "Start" menu and click "Computer" to launch the default Windows file manager.
Use the file manager to navigate to the microSD card and open the TTMENU folder.
Locate the wallpaper file, right-click it and select "Set as Desktop Background" to set the image from the Nintendo console as your wallpaper.