Trace a copy of back and front bodices. Draw the new hem line at underbust on both pieces.
On back, erase the dart and discard it from center back. Reshape it to have a 90°angle between center back and waist line and center back and neckline.
On front, widen the dart from waist to underbust making it 3cm wide all the way in this section, then shape it to bust point. Draw the upper part of the cup and widen shoulder dart by 1cm at this point, then blend to shoulder line. Draw the bottom cup line from dart to center front, curved.