The band? You usually can't. You may be able to sew it longer but that would mean you would have to probably buy a new hook which you can get easily. Also, go to your fabric store and see what they have. I think I remember seeing things to adjust your bra at my local JoAnns so I'd check there. If not, then do it yourself.
Go get fitted. It sounds like you're a 36B. You have to remember that two women with the same breast volume may wear different cup sizes because of the difference in band size (a 36B is approximately the same volume as a 34C)