I did it myself in the driveway on a 30ft 5er. Dexter makes a flip kit for about $55 on Amazon. You do not need to weld the new saddles to the axle but it is better if you do. Just a couple of spot weld will do it once you are sure the saddles are in the right position.
You will also need 4 jack stands or cribbing to hold the trailer up, a rolling floor jack helps but is not necessary, to position the axles, and watch a few youtube videos on the subject. Some of the lift methods are pretty interesting but not something I would try. One guy used cinder blocks on their side with a jack stand standing on the hollow portion of the block :E I just jacked it up and put the jack stands under the frame close to the spring shackles.