Upper control arm mounts/shock tower
I haven't used that particular replacement part, but as far as how to go about replacing them you're going to need to take a lot of very careful measurements.
You're going to need a very flat area to work on. Then level the chassis, and use a string with a weight on the end to drop reference points onto the floor. You'll also want to locate the control arm mounts from several different land marks that aren't going to move during the replacement process. All that has to be done before you remove the old towers.
Once that's done you'll need to remove the old towers/mounts while not moving or disturbing the rest of the chassis. Then clamp the replacement parts into place, confirming your measurements from your previous landmarks and checking the reference points on the floor with the string/weight.
Cutting out the old metal and welding in new stuff is easy. Taking all the measurements and confirming them will take the most time, and it's just tedious. But you want to be able to align the car afterward. If you haven't done that kind of work before, just go slow and take lots of measurements. You know, "measure twice, cut once" as they say.