If you look at the front of the front sight base you will see a witness mark on the front sight base and front sight drum that should line up.
The sights were set at the factory and once set a staking tool was held on the front sight and hit with a hammer. This locked the front sight drum in place by displacing metal and bending the drum every so slightly. This is why you can't move the front sight drum as it takes quite a bit of force to get it to first move. To keep from leaving marks on the front sight drum use a brass punch or the most cost effective(cheap),field exspeident tool, a 3/16" steel punch with a fired 22LR case slipped over the end. Use a 2 or 3 pound hammer and whop the hell out of the punch. Once the drum makes that first move then all you will need is to tap the punch with the hammer to get it to move farther.
Remember the sights were set at the factory so if you move the drum to line up the witness marks it should be sighted in for windage. Then all that will be needed is to screw the front sight post in or out to set the elevation.