Hi Viz Spark II shotgun bead?

[Esox357]

Hello all, I just bought a Hi-Viz Spark II shotgun bead for my Remington 11-87 Light Contour.
The problem is that the Hi Viz bead is already threaded with a post from the factory and came with additional threads for different sizes. I can't figure how to get the factory thread off to put in the proper replacement thread that it came with it? The posts are threaded on both ends that fit into the sight iteself and then to the thread on the shotgun.
I was going to use pliers to grip the post and try to remove the factory installed threaded screw but didn't want to damage it. Any one have any experience doing these? I know it shouldn't be this difficult. Any other sights you would recommend?
Worst case scenario I will have to find a different bead for my shotgun or order through rem a new bradley bead. Thanks. Esox357