Facing the bottom of the grip, turn clockwise since the threads are in the top brackets. Use or devise a pin wrench. Pins must fit tightly into the holes. Using just two short pins made from spring steel wire, I often drill the holes a bit deeper to give the pins resistance against tilting. Also, drilling the holes to fit the pins tightly if the holes are already buggered.
Turn slowly initially, reversing direction alternately until the stake depressions have conformed to the threads if the grip has been staked to the bracket.
Sometimes the grips are tight and sometimes not. Luck of the draw.
Move the grip slowly when starting and get a feel for it the tightness and unscrew it according to the feel.