How to change background in twitter

To customize your own design:

    If you want to upload your own background image or customize the sidebar and color scheme of your page, follow the steps below.
    1. Sign in to your account.
    2. Go to your Settings and click on the Design tab.
    3. Scroll down to the Customize your own section.
    4. Click on Choose file to upload a background image. Images justify to the top left of the screen. You cannot stretch your image to fit. It will display as the size you uploaded (file must be smaller than 800k).
    5. Check the box to Tile background if you want your picture to repeat across the background.
    6. Choose whether your Background position will be left, center or right.
    7. If your image isn't very large, choose the background color that will show behind the image.
    8. Choose a color for links.
    9. Choose a black or white transparent overlay.
    10. Click Save changes.
    Note: Background images must be in PNG, GIF, or JPG format, smaller than 800k. If your image's file size is too large, use an image editing program or web app to shrink the image.Animated GIFs are not supported as background images. 

    To customize your design with a premade theme:

      1. Sign in to your account.
      2. Go to your Settings and click on the Design tab. 
      3. You will see a Pick a premade theme menu, select a premade theme by clicking on the design you would like to use.
      4. Click Save changes at the bottom of the page when you're done. It's as simple as that!