Unscrew the forend nut that holds the forend to the barrel nut. Not you can pull forward on the rail to free up the anti-rotation pins. Pull those anti-rotation pins out and you can now scoot the rail forwards and backwards a bit as well as rotate it so that you can line up the pins with one of the slots in the forend. Support the muzzle end of the barrel and make sure you are driving out the front sight pins in the correct direction. Not complicated unless you try to make it so.