Not sure about the year you have, but on my '82 it's a peice of cake. Jack up the car (jackstands of course) remove the lower bolt, the three upper bolts and slide it out, strut and spring assy in one chunk. Most auto stores will handle the spring for you, just take them the assy and your new struts. They will charge a few bucks to do it, but if you have never worked with auto springs before it may be in your best interest to let a pro handle the springs.
I'm surprised that no one has responded to this yet, but the rear suspension on a 76 Z is completely different from that of an 82 ZX (the main difference in fact). The 75-78 Z's, and earlier ones, had a strut assy all the way around that incorporates the spindles or axle stubs into the housing, rather than into a separate arm. There's alot more work in the older Z's to getting the struts out. It's not hard to do, especially if your undercarriage is in good shape and free of rust, but be liberal with the WD-40, the bolts can be quite rusty. I'd recommend a good manual, at least a Chilton's or Clymer, but your best bet is the factory book. 75-76 are both covered in the same one.