What size to choose? I have 380cc Motiva implants and I want bigger. I am 5'9, 175 lbs. (photos)

Thank you for the question and pictures.  You will find that online consultants will not be able to provide you with specific advice in regards to selection of specific breast implant size/profile. Ultimately, careful communication of your goals will be critical.
Generally speaking, the best online advice I can give to ladies who are considering revisionary (upsizing) breast augmentation surgery (regarding breast implant size/profile selection) 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 "C cup” or "up one cup size" 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 plastic surgeon to use his/her years of experience/judgment to choose the breast implant size/profile that will best meet your goals.  Again, in my practice, this decision is usually made during surgery ( after the use of temporary intraoperative sizers).  Viewing the patient's chest wall in the upright and supine positions, with temporary sizes in place, help select  the best breast implant size/profile for the specific patient.
I hope this helps. Best wishes.

It would be hard to determine which implant size will be best for you without an in-person examination. Your best resource of information regarding this would be your surgeon. He/she knows your condition best.