There are several detailed writeups with pictures on rv.net. Wager there are a few here too. Did mine on my old trailer several years ago and it was one of the best investments.
The dexter kit is awesome and has great instructions. The "spacers" are bolts that are attached to the new spring pads and are adjusted against the old spring pads. I used c clamps to hold everything together while making easy adjustments. Do you have access to a mig welder? That allows you to tack the new spring supports in place. Can be done without, but it makes it more difficult keeping everything in alignment. Make sure you gather all tools and parts before starting. Have plenty of support for the frame. I raided several garage sales and found several sets of Jack stands cheap. Used old 6x6 posts on stacked concrete blocks as well. In all I had solid support along the frame every 5-6 feet. Beware of any wire harnesses or gas lines under the frame that could get pinched.
Since you have the whole trailer up and both axles off, think about replacing/rebuilding the bushings. Went with a wet bolt kit and went from that squeaky trailer in the park to smooooooth and silent. If you go that route, a impact wrench makes disassembly extremely fast. Keep the old bolts as they will help to gently install the new bushings in the spring eyes. Also taped off the data stickers and gave both axles a new paint job to protect from rust. In all a full weekend job.
The lift kit solved the dragging bumper, leveled out the trailer with my tall truck (stinger was at its lowest setting), and bought me more room in the wheel well for the next load range sized tire. Saw no adverse affects in drag or handling.
Can add more detail if you want, but I am probably boring everyone to death.
2015 puma 295bhss
2009 ram 3500 6.7l ctd