Lemoyne, You cant!

I was forced to buy a set of plastic sights in 2006? when the fiber optic broke on my original sights. You tighten up the screw and the plastic sight turns into a U and with enough force, you can slide them up the ramp with thumb-index finger.

Any time you get a gun with plastic sights, take them off and throw them in the trash because they are just flat out junk. Plenty of good affordable open sights out there to choose from.