Your mammoth implants are just way too large for your frame and tissue and may not move much more than they have done. However, they do need to be supported so they don't drop down to your lap.
Your implants appear to be in the proper place, but your breasts have sagged. You can have a lift, with or without smaller implants, or place the implants just behind the breasts so you will have larger and sagging breasts.
You might consider going down to 200 cc's. The smallest is 150 cc's. However, if you have little breast tissue, implants will look better behind the muscle.
