I am not happy with the size of my butt implants. I want a bigger size. How big can I go?

My surgeon recommended 390 for me after that he measured my buttocks. Under the muscle. There is not a big difference. I’m not satisfied with the results, the measurements are okay horizontal but vertical, the implant “stops” in the middle of buttock and it creates a small bump which I don’t like. It feels like it’s to small vertically. I want to go for a bigger size, but how big can I go? I did the surgery 7 months ago, is it possible that my buttocks are ready for bigger implants?