1. First place a ruler along the center back seam and extend the line downwards a bit. This will show the point where the center back seam starts to curve. From that point, which I call the "turning point", draw a horizontal line over to the side seam. (This line will be parallel to the crotch line and perpendicular to the grain line.)
2. Cut the pattern along this horizontal line leaving a "hinge" just at the turning point. Open a small wedge. Very little is actually necessary to create a pretty big change so make this wedge small. A 1/2 inch opening at the side seam is a significant but reasonable alteration. How wide to make this opening of course depends on the body shape one is fitting. It is best to err on the side of too little at first as too much will generate a pattern that will produce new horrible fitting problems.
3. Opening the wedge has changed the angle of the center back seam. If a line is again drawn using a straight edge along the center back seam this shift will be obvious visually on the altered pattern. The grain line of the upper hip will need to be redrawn which is done by simply extending the line of the lower part of the pattern upwards.
What about the front of the pattern? With a small alteration I find that the extra length can be added to the top of the front pattern's side seam. For my body shape I add at the top and curve down to center front of the original pattern. The side seam curves are then compared and made similar and smooth.
