You need a coil spring compressor and alot of patience. You'll slide the spring compressor down into the spring from above and use a wrench to compress the spring. Then you'll be able to slide the compressed spring out through the wheel well.

Here is a good web site with some basic info

Look here - this shows how to build your own spring compressor
DazeCars, Home Made Bolt in Spring Compressor

I used this kind with a couple of metal spacers on it -