Saline Breast Implant Reduction

Downsizing your breast size is best achieved with new implants, not removing the fluid from the existing ones. In order to give you the best cosmetic appearance, you may also require a breast lift as well to tighten the pocket of the implant. Another option is a lift alone without any implants, but these options are best discussed with your surgeon so that he can discuss with you the pros and cons of each choice. Simply removing saline from your existing implants, however, is not a good choice for all of the reasons already stated.

I would not recommend this as the chance of  old implants rupturing in the near future doesn't warrant the risk of a subsequent operation in the future, plus you will probably need to make your pocket smaller, any warranties that may be in effect are voided, and putting too little saline often causes rippling/waviness and premature rupture. Check out IDEAL implants for saline implants that feel like silicone.

If you currently have 375cc saline implants and would like to end up with 225-275cc you will definitely need new implants as the implants can only be filled to a certain volume. Ex. your 375 cc implant can be filled from 350-375, but it can't be deflated all the way down into the 225-275cc range.
Converting from 375cc to 225-275cc could possibly leave you with some excess skin or possibly affect your nipple position. You should be evaluated by a board certified plastic surgeon to determine the need, if any, of a potential breast lift, or to decided if the procedure needs to be staged, i.e. first remove the larger implants then a few months later, after the skin has contracted a bit, replace with smaller implants thus avoiding the additional scars that a lift may require.
Best wishes!

If you would like to decrease the size of an implant, this will require another surgery.
You may be able to keep the same implant if you only want a small amount removed. For example, 25-50 cc, depending on the implant.
Implants have a range of saline they need inside in order to maintain their shape. If you go below this range, the implant will collapse on itself. This will depend on the implant you have and how much saline was put in during the initial surgery.
Thus, if you want to remove a large amount of saline from the implant, you will need to replace the implant for a smaller one.

You can adjust those implants by 50 cc, that is, if they were 325 filled to 375. This is not a significant reduction.
In general, I recommend a reduction by at least 100 cc to have a noticeable difference. At times also if you do a significant reduction you may also have to tighten the skin (do a lift-mastopexy). Good luck.