Great question Carol. It isn't as easy as removing a background image from a profile. In a profile you just go to edit mode and uncheck the background image box. With a space page, the background image is set via the image. If you know where the image is, go to it and on the bottom right, look for the section "Set as background image" and deselect your space page.
If you can't find the photo, just go to any open photo, add your space page to that photo and set the 'new' photo as the space page background image. This will replace the old image with the new. Then, simply deselect the new image and then remove the space page from that image and your space page will not have a background image.