Size of implants whether it is for a breast augmentation or butt augmentation is one of the hardest decisions for patients to make prior to their augmentation. In general patients are extremely happy after their augmentation but at times wish they had gone bigger.
Number one I would advise you to spend time talking to your plastic surgeon about your butt augmentation that way you can get the appropriate size during your initial surgery. However even with that said there are times that patients want larger implants than the body can accommodate at the time of the initial surgery or patients later wish to be larger.
I typically have patients wait at least six months before I will exchange the implants for a larger size. One this allows time for the swelling to completely resolve so that patients can see their final results before making a decision on a new size. Second waiting this time allows the skin to stretch making it easier to accommodate a larger implant. Lastly waiting this time will allow the tissues on the inside time to settle so that the second surgery will be easier and safer.
Please discuss this with you board certified plastic surgeon that performs a high volume of butt augmentations.