The botton bolt on the hub can sieze in which can cause it to snap, then you are in bother. What I have done in the past is undo the top shock absorber mount inside the boot, unbolt the anti roll bar link, then get a mate to stand on top of the rear drum to drop it as far down as possible while you lever the spring out with a lever bar. It also helps to put spring clamps INSIDE the spring, up through the hole in the lower arm so you can clamp it as far as possible.

The new spring should fit in a bit easier because it is shorter.