To move the waist position higher/ lower or lengthen/ shorten the front and back rise. Draw a straight line from CF at seat level, slightly below the fly if it is not marked. It must be 90 degrees to the grainline. 

Measure from the top of the waist at side front and mark the same distance at back. Draw this line to the back rise seam, where it becomes 90 degrees. 

Cut, then move apart to lengthen or overlap to shorten. Adjust the pocket bag and front zip if needed, and don’t forget the shape of the connections where required.