Right click on the image, click "set as background"/"set as wallpaper" and change the position to "tile". If you left click on the image you can then go to "file" and "save as" to save the file to you hard disk
Click on the numbers that are the same as your screen resolution, right click on the image, click "set as background"/"set as wallpaper" and change the position to "center" or "stretch". If you left click on the image you can then go to "file" and "save as" to save the file to you hard disk