You may find that even when you get the screw out, the sight itself won't easily move. The dovetails can be tight and there may be some Loctite or equivalent in the dovetail. Springfield did this on a new Garrison I bought. Just adjusting the sight gave me fits, let alone removing it. In short, you may need a good sight pusher.

It does sound like you haven't done this before, OP. Seeking advice like you're doing, and perhaps getting some hands-on assistance is wise.