Cannot apply background image with theme

I’m using ChocoTheme with latest wordpress. It has a tool (button in theme’s control panel to add an image from my pc to use as the blog’s background instead of just the background color. It won’t work. I’ve also tried uploading the image to the images folder of the theme and linking it in the code in styles.css custom editor and that won’t work either. Any ideas? Should I paste my code i’m using? Thanks.