There are TWO ways....both involve unhooking the front sway bar.
the NORMAL way everyone does them, is unbolt the two strut bolts from the knuckle with a jack under the control arm. Lower the jack (make sure your caliper is unbolted and secured out of the way or else you could fuck up the lines). Pop old spring out, swap over isolators (if you want) and PRY the SHIT out of the new spring to get it in.
The OTHER lesser heard of way (and the way I do it) is to unbolt the CONTROL ARM (or A-Arm) from the k-member...again with a jack positioned under it and drop the spring out THAT way, relying on the pivot of the ball joint. I found you get ALOT more sag out of the arm meaning less fighting of the spring's pressure when you jack it BACK up to reinstall the bolts. I find THIS way is a MILLION times easier. This was putting in Eibach Drag Launch springs so putting in DROP springs might be easier the when unhooking the strut. Lineing up the a-arm holes is just a matter or jacking the arm BACK up to the right height and moving the jack, in or out, as you see fit to reinstall the bolts.
Unbolting the strut from the top is NOT required!