Uploading your own background image

Step 1: Go to Design > Template Designer > Background and click the dropdown button under Background Image heading.

Step 2: Click Upload Image

Step 3: Click Browse button and select an image from your computer. 

Step 4: Set the background’s alignment, tiling and scrolling.

Step 5: If you're satisfy with your background, then click Apply to Blog.

That's it and you're done! :)