Sorry for the delay in response. I’m assuming the bodice section and skirt section of the pattern is a single piece and not two separate pieces. If the dress is fitted, look on the pattern and see if there’s a line indicating the waistline (there should be) and fold on this line, then fold up however much you need to adjust. One side (the center front/back) is normally the straight edge, but you might have to do side seam line blending to give yourself a smooth line. It might be difficult because 4″ is quite a bit. Definitely make a muslin, at east of the bodice section to make sure it’s a good length for you. If the dress is really loose and not fitted, you can probably just take the 4″ off from the hemline and you’ll probably not notice the neck to waist measurement. Hope that helps.