Size of background images

[tokkolo]

I made a website design in Photoshop and sliced it in Image ready. These background and header images together are about 80 kb. I think that is a lot, since my website exists of jigzaw puzzle of photographs I made. On every page there will be tumbnails of the puzzles. These tumbnail will take loading time, so I would like to keep the the background images as small as possible.

When I save the slices in Image Ready I don't have (or see) any option to lower the quality (and the size) of the images. Does anybody have an idea on how I can decrease the size of my background and header images when I save/export the slices I've created?