Adjusting the sights on an M4 can be done using your fingernail or a round of ammo but get it done much quicker, easier and safer with the M4 SAT sight adjustment tool.  This easy to use tool simply pushes down onto the front sight post.  Rotate the click wheel on the tool clockwise to lower the post and counterclockwise to raise the post.  You can hear and feel the tool click.  Comes in a 2 pack.