How can I change Start screen picture HTC 8X?

[WPCentral Question]

I have a HTC 8X phone and install a new 8.1. version. One of news of this version:
Tile background on Start screen- Tiles fit together like puzzle pieces to display the full image.
In Transparent tiles maker- I must go in Setting- System- start+theme and change a photo to Start screen. But It's doesn't work .
What can I do wrong?

 

[N_LaRUE]

Have you read through this?

Personalize my Start screen and theme color on Windows Phone | Windows Phone How-to (United States)