Hello
To amend you can add the following to the Custom CSS field of your templates parameters (Extensions -> Templates -> [YourTemplateStyle] -> Custom CSS)....
#body_bg {
background-position-y: 0 !important;
background-size: cover !important;
}
This should resolve the blurred issue. If you would still like to swap the image let me know and I will provide the needed CSS. Please include a URL to the image you wish to use.
Ciaran