1. Make a copy of your background

You do this because when your image is titled Background as shown on the left, you cannot move it, and you cannot separate the image from the background. Do you see the padlock on the layer menu? That means you can't change a lot of things to it, like the blending mode and opacity.

So what you do is drag the layer titled Background with your mouse, over to the create new layer button, down there. It's the second most right button, besides the dustbin.

That action will make a new layer titled Background copy (image on the left). Now you can delete the layer titled Background, and start using the Magic Wand tool.

2. Let the magic begin!

Click on the Magic Wand tool, and then click on the part of the image that you want to delete. Take for example, this white background in this image on the left. You will see moving dots on your image. Then press the delete button on your keyboard, and walla, the background disappears!

Keep doing this, while making sure that you don't accidentally delete anything important! If you find a part that's difficult to clean or delete, you might have no choice but to manually erase it with your erase tool. I know there are other ways of doing this, like using the mask tool, but I don't know how O_o Can somebody teach me? :D

Now that you've deleted the background, you can start work on it, and make your very own wallpaper! Cheers, have fun!