Sample: 3/4"x4-1/2" MWLN R-12-4C Toolholder, RH, #2316-0008

Loose the upper bigger nut screw. (Counter clockwise)

After the upper bigger screw looses, start to loosen the small screw inside the insert.

All the screws need counter clockwise to loosen, while the clockwise will made the screws tighter.

The screw inside the insert does not have to be too tight; otherwise, the screws will be stripped. Then you need screw extractor to take it off. 

However, the upper bigger nut screws need to be very tight.