Step 1
On both back and front, reduce a couple of cm at the hem.
Get a sleeve, cut it in half and align it to the bodices matching the notches to draw the sleeve/collar band.
On back, draw the new neckline and reduce the dart discarding part of it from center back.
On front, discard the waist darts from the sides and draw the new slanted dart lines from bust points to the side seams to manipulate the shoulder darts.