Adjusting the shoulder width

The shoulder length of a garment could be altered by simply taking away from the armhole edge - but this will affect the shape of the armhole, making it difficult to insert a sleeve. Instead try this method from Claire Tyler.

Mark the stitching lines onto the pattern. When altering a pattern it is always more accurate to use the stitching lines. (A)

Take the measurement of your shoulder and check it against the pattern, remembering to measure the stitching line only. 

Draw a line from the middle of the shoulder, to just before the armhole starts to curve - this will often be where there is a notch (B)

Cut along the line from the shoulder to the armhole but don't cut all the way through - this will create a pivot point at the armhole (C)

If you need to make it longer, open the shoulder by the amount you need and add some paper in the opening (D)

Re-draw the shoulder stitching line from the neck point to the shoulder point, and add the seam allowance (C)

If you need to make it shorter, overlap the shoulder by the amount required (F)

Re-draw the shoulder stitching line from the neck point to the shoulder point, and add the seam allowance.

Remember to make the same alteration on the front and back pieces.

Claire also shows this techniques in this video