1. Trace your pattern along the neck, shoulder and armscye. The second picture just shows what you need to trace without the original pattern in the way :)
2. Draw the line for the new side seam as shown in the picture below. The angle of the line is personal preference ... the red line is the one I used for the rest of the illustrations. For a narrow aline move the line closer to the original pattern piece (green line) and for a wider aline angle it further away (blue line).
3. Draw a perpendicular line from the bottom of the armscye across to the center fold line (the edge of paper in my picture)
4. Determine how long you would like your finished top/dress to be (be sure to add a hem allowance) and make a mark on your pattern. In the picture below, this is the bottom of the line that measures 14". Then measure from the line drawn in step 3 to the mark you just made. For me, this was 10 3/8". It is not necessary for you to draw the blue lines like I did ... they are just for illustration purposes.
5. Transfer that measurement to the new side seam drawn in step 2 and make a mark. Again, you don't need to draw the line ... that's just overkill on my part :)
6. Draw a gently curved line from your mark along the center fold and the mark along the new side seam.
7. When you draft the front bodice piece, make sure to use the same measurement for the side seam as you did for the back piece so they line up correctly when it's time to sew. Unless asymmetrical is the look you are going for, in which case, you can use any measurement you want :)
And that's it ... you are done! Enjoy your new pattern :)