Although bras are designed to fit women of many sizes, you can still have trouble finding the perfect fit as the band or the straps may be too small or large. With basic sewing skills, however, you can make some adjustments to your bra. Altering Bra Straps
Shorten the bra straps as far as you can with the strap adjusters located on each side. If the straps are still too long and you can not shorten them any more, then you can modify the straps.
Fold over the excess length in the strap while you are wearing the bra. Do this for the both straps. Secure with a safety pin.
Sew the strap in place with a sewing machine. Use thread that matches the color of the bra.
Adjust Bra band
Determine your band size before you modify your bra. Wrap a tape measure around your body, just beneath your breast. Ensure that the measuring tap is parallel to the ground and is snug. If your measurement was an odd number such as 33 inches, round up to the nearest whole number. In this case, 34.
Take in the band 1/2 inch for every 2 inches of difference between your measurement and the bra measurement. For example, if the bra is a 36 and you are a 30, then take in 1 1/2 inches of the band from each side of the bra.
Fold the band underneath your underarms. Make sure the band is snug around your body, but not too tight. The folds should be facing outward so they do not rub against your skin.
Sew the tucks in place with a sewing machine. Use thread matching the color of the bra. Stitch over the folds three times to ensure it will stay.