The pins for the rear sight base? Just push them out with a punch. I highly recommend taking the rear sight base off completely. There is a 3/8" dovetail under there which I mounted a 3/8" one piece airgun mount to. It holds zero great. The mounts that replace the rear sight leaf never seem to hold.
They can be pretty hard some times. Take a torch and just heat up the area lightly (not red hot) and really give your punch a good whack. They'll come out. Also, just so you know that mount will not work if you are still using the original stock. You would need the offset version of it.