First thing, everyone and their grandma will tell you that this is too dangerous, you'll kill yourself or shoot your eye out, or launch the spring through the wall and kill your dog or something. The way these springs are setup, you cannot hurt yourself doing this unless you are incredibly stupid. So as with all my how-to's, incredibly stupid people should probably ignore this entry, or else we'll just chalk it up to natural selection. As long as you take the center bolts of the strut out AFTER the spring is compressed, there is no risk of bodily injury save a few skinned knuckles, possibly.
You'll notice there aren't many people on this board who do their own work. Here's how it goes - you can just cut the strap on the struts, it's no problem, that strap is just to keep them compressed so they fit in a smaller box without poking out the side. When you cut the strap they'll slowly let themselves out to full length. Spring seat goes toward the top, spring goes on top of it. To get your existing strut off the car you should do this wheel off (obviously) and car on jackstands - then detach the top first, (under the hood on the strut tower, just the bolts around the outside, leave the big middle one alone for now) once it's loose from the top, take the bolt out of the bottom and take it off - then put one spring compressor on each side of the spring and compress the spring until there's no more pressure on the top of the strut(the part you took out of the strut tower) and once that's done, take out the center bolt, and the top will come off. Then you'll want to gradually (aiming the old strut away from you) release the tension on the old spring so you can get the compressor off if you're changing springs, put the old or new spring on the new strut, screw your old top onto the new strut, and then decompress the spring. Then screw the new strut into the car, and you can use the weight of the car to compress the strut into position. Repeat for both or all 4 wheels as the case may be. The back strut towers are in the trunk. Have fun and aren't you glad you saved yourself $300 for something you can do yourself in 2 hours?