Even though I don't know this particular car I think the Ford Laser is a descendant of a Mazda and therefore will most likely have McPherson struts up front. In such a case you have to remove the complete front strut. Then compress the spring with a spring compressor because the spring is still under pressure even without the car's weight (you absolutely have to use a proper spring compressor, if you try a bodge job the spring might slip and this might result in serious injury). While compressed you can take apart the strut, decompress the spring and mount the short spring in the reverse order.
Up rear I'm not sure. But it might be that the rear springs are still under pressure with the car jacked. In this case you'd have to use the spring compressor again to compress the spring before loosenig any bolts or the spring might jump at you!