keep in mind at this point that the only way to enlarge them would be to stretch them via whatever means.. (breast feeding will do this from constant suckling for instance) and is probably not worth the discomfort in the end, by whichever means you choose.
there are some women who have had success with using breast pumps to enlarge their aereola's, but it is not healthy nor recommended.
i think whatever you were born with should be beautiful enough for you and anyone else who happens to be concerned.
if this is for reasons to attract the opposite sex, I would like to point out that most guys like your aereola to be tiny, petite... not large...
if you are concerned that they may be underdeveloped and not just small, consult a doctor. There ARE aftermarket products such as bloussant that will increase breast size and in your case MAY cause your aereola to grow. (as it contains the same breast growing hormone produced by your body during puberty)
I am all for becoming more aesthetically pleasing and attractive, but always be sure to run opinions by others before you make decisions.. chances are you will find your bodyparts are just plain ol' perfect...