MNpurple

I just bought a Nova and it has the standard red fiber optic site at the end of the barrel. I would like to take this off and replace it with a green one. Is the red site glued on or is it screwed into the vented rib? I tried to turn it, but it was very tight and if it is glued on, I dont want to break it. The green one I want to replace it with has a small screw on the bottom of it that screws into the rib, and I suspect that is how the red one is attached? Any help would be great. Thank you