You now have 300 mL implants, and feel they're too small. If you fill the implants more than the manufacturing companies suggests, the warranty is voided. Also if you add more fluid to your existing implants, the warranty is voided.To increase your breast size you will need new implants. I suggest increasing your size at least 100 mL to make an additional operation worth your while. An excellent alternative plan would be fat injections in addition to your present implants, providing you have areas that you would like liposuctioned. This would be particularly suitable if your present implants are behind the muscle. Thank you for your interesting question.