Loosen the spring compressors on the old spring, using the same method as when tightening them.. no more than 5 turns on each side, and keep the pressure even.
If you've looked at H&R front springs, you'll see they are pretty short. The stock ones are not short at all. They are about double the length, so it will take a while to take the pressure off of the old spring. However, once you've done that, grab a new front spring, make sure the writing is facing up, and start to compress that one. The front springs are marked with a (F).
Do the same as on the factory spring. Grab 3 coils, opposite each other for each compressor, and have the bolt head facing up. Begin compressing that spring, using the 5 turns each side method, until you've tightened it as far as you can.
Place the new spring on the strut sticking out from underneath your front fender. Make sure you ease it over the shock boot, and if you pull the boot down, make sure you slide it back up onto the boot mount after getting the spring seated on the rubber mount.
Now you can replace the top strut hat, washer, and swivel. If you've compressed the spring enough, you should have plenty of room to grab that nut and a 19mm socket and tighten it back down. Make sure you have the spring rightside up and seated properly. Once tight, replace the plastic cap.