First you need to remove the struts. To do this you have to jack up the front of the car & block it up. Remove the wheel,The brake caliper, sway bar link to the strut & then unbolt the top & bottom mounts for the strut.
After you have removed the strut you will need to compress the springs before undoing the top. There is another nut under this assembly that holds the spring caged to the strut assembly.Be very careful here as when you pull it apart there is a lot of small bearings that will go everywhere. Fit your lowered springs & then reassemble. Note that if your springs are too low that when you attempt to reassemble it if there is no tension on the spring the bearings will keep falling out. I have just done mine & I fitted a K MAC top strut bearing assy which will solve this problem. Unfortunately it costs $400 so that is up to your budget.