Customizing Windows 8 Metro Background Image via Start Tweaker
1. First of all you have to download Windows 8 Start Tweaker. You may download it from here
Save it to your computer and then right click on it and select Extract All to extract it.
2. Next, You will see the extracted folder to the location where you have extracted the zip file. Open the application file (.exe) Win8StartTweaker by double clicking on it.
3. On User Account Control box, click on the Yes button.
4. Click on the English flag at the bottom right to show application in English language
5. Click on the Metro Background Image
6. Next, locate the image file you want to use and click on the Open button.
7. Next, You will see your image. Click on the Apply button.
8. Click on the Yes button to logg off and see the new background used.
9. Finally you will see your image as a wallpaper in Windows 8. That are the complete steps to change wallpaper in Windows 8. If you want to restore the default Windows 8 wallpaper then run the Windows 8 Start Tweaker again and click on the Reset button.