If you have a fairly new M4, in theory you will only need a metric hex wrench and a heat torch to remove 6 flat head hex screws on the upper rail. Some vendors will include the wrench and 6 extra screws in the very likely event that you might strip them. (The threads are welded with lock-tite). The recommendation is that you heat the screws with torch, then very simply back the screws out. Yeah right! I stripped three, and now the unit is at a local machinist for damage control. t's a bit tricky, and you have to be careful not to overheat the aluminum.
If you have an earlier version M4, (before the barrel design had changed), the unit will slip right over it and into place.
You won't know, until you make the purchase unfortunately.