I removed both factory sump splasguards, don't remember if they get in the way or not honestly, but regardless, they become redundant dead weights with the Asfir guard installed. I also removed the small plastic spoilers in front of the wheels. Useless as well, and you can actually break them off road. Regarding the install, I am afraid I forgot how I did it... Pretty sure I started with the larger rear section though, very loosely attaching center and rear sets of bolts first. IIRC, the front anchors for that plate are shared as anchor points for the front guard as well, in an interesting stacked arrangement of plates, bolts, washers and locking bars that need to slide into a chassis rail just right before the whole thing can be tightened in place (there were no instructions with mine either, but a one-page packing list / diagram kinda showed where the various nuts and bolts went.) Perhaps Ivan, who just installed his, has a more vivid memory of the procedure. Once you slide under the car and start playing with the guards to see where they bolt on, the whole process will become fairly clear.
A floor jack will help tremendously to lift the heavier of the two plates up against the chassis to bolt it on. And strategically position a. couple of jack stands before you venture under the car. Never trust the air suspensions with your life. I know it's common sense, but some folks don't seem to have any, they just put it in off road height, open a door and figure that's all the safety steps they need to take before working under the car.
Umberto , could you elaborate on the locking bars placement, Do I have to remove front OE plate as well or just the large one?