Larger to smaller: 650cc high profile to smaller moderate plus/moderate

Overall you have nice shape and symmetry.  If you go down 100-150 cc you will not need a lift and only require tightening of the capsule to make sure the implants are in the proper position on your chest wall.  If you are still experiencing capsular contracture this may require a more involved procedure.  

Your likely to go down in size between 100 to 200 cc. It is important to understand that changing your 650cc high profile implants to about 500cc moderate plus implants will reduce some of the size in projection but will essentially keep similar width of your breasts.  I think it is important for you to have an in person consultation with a board certified plastic surgeon to carefully review your specific goals and expectations. I recommend seeing a 650cc high profile sizer and compare it to different sizes in moderate plus and high profile to help you decide with your surgeon your final objectives. If you have a true capsular contracture, I would highly recommend you use Strattice acellular dermal matrix in the repair to dramatically reduce the chances of recurrence. Best wishes for your successful results. Dr Sam Gershenbaum

Thank you for the question and pictures.  
Keep in mind as you are thinking about your goals that sometimes adjustment of the breast implant pockets (capsule adjustments) may be necessary to achieve the outcome you are looking for.   Whether or not the adjustment of the breast implant capsules will be necessary will mainly be dependent on your physical examination; specifically, factors such as the amount of redundant skin, quality of skin elasticity,  and how much you downsize will be important.  
Generally speaking, the best online advice I can give to ladies who are considering revisionary (downsizing) breast augmentation surgery is:
1. Concentrate on choosing your plastic surgeon carefully. Concentrate on appropriate training, certification, and the ability of the plastic surgeon to achieve the results you are looking for. ***Ask to see lots of examples of his/her work.
2. Have a full discussion and communication regarding your desired goals with your plastic surgeon. This communication will be critical in determining breast implant size/type/profile will most likely help achieve your goals. 
In my practice, the use of photographs of “goal” pictures (and breasts that are too big or too small) is very helpful. I have found that the use of words such as “natural” or "significant difference” or "D cup" etc means different things to different people and therefore prove unhelpful.
Also, as you know, cup size varies depending on who makes the bra; therefore, discussing desired cup size may also be inaccurate. 
3. Once you feel you have communicated your goals clearly, allow your chosen plastic surgeon to work with you in determining the best plan to achieve your goals.
I hope this, and the attached link (dedicated to revisionary breast surgery, specifically downsizing breast augmentation surgery concerns), helps. Best wishes.  

Best to seek a few in person opinions from ONLY 'private practice' boarded PSs in South Florida. My guess is exchange with open capsulotomy/ectomy (plus MUST drain!). Decrease in size by 50 to 75 cc's only. Read Dr B