A woman's jacket can be made larger by letting out some of the fabric in the seams. Even a 1/2 inch on both side seams will add an extra inch to the width of the jacket. Some women's jackets also have double side seams or a seam down the back to allow for a more fitted look. In this case, the jacket can be made even larger.
Remove the stitches from your jacket's arm and side seams, using a stitch remover. If there is a seam down the back of the jacket, remove those stitches as well. Do not substitute a stitch remover for scissors as this can permanently damage the fabric of your jacket. Remove any remaining threads by hand, ensuring that all the stitching is removed.
Draw a line on the inside of the seams to indicate where your new seams will be sewn. Make sure to use a ruler so your lines are straight. Also, make sure to leave at least a millimetre of fabric from where you will be making your new seam. This will prevent the new stitching from ripping or showing through the seams.
Sew along the lines to close your seams, using a thread colour as similar to the colour of your jacket as possible. To create a straight and smooth seam you should use a sewing machine; however, if you do not have one you can do this by hand. If you are sewing by hand, take your time and focus on making as straight of a seam as possible. Also, space your stitches out evenly to create a smooth line.
Iron along your new seams to release the creases left by the old seams. This may take some time as the seams will be rigid. If the material of your jacket is strong, you could add some water to the seam before ironing. This will create a steaming effect that will help with releasing the crease. If the material is delicate, use a clothing steamer.
If your coat has buttons down the front, you can remove the buttons and reattach them closer to the centre. If holes are left in the fabric from where the buttons were attached, find larger buttons that will cover the holes.