I’m going to teach you how to mount a red dot sight on your Ruger AR-556. You’re going to need two tools, an Allen wrench and a screwdriver. The first thing you want to do is remove the front sight post by loosening the set screws with your Allen wrench.
Now you can slide off the rear site leaf spring assembly and then reattach it after mounting your scope onto its base plate. Then use your screwdriver and loosen the set screws holding down the rear sight leaf spring assembly (which will allow it to move up). Finally, tighten all of those screws back down using both wrenches – easy peasy.