Reshaping/filing down from crowns & composite resin. (Photo)

So both my front teeth have crowns on them, I've had them for about a year, I never really payed attention to the way they looked at since I usually never smile with my teeth showing but now in pictures they almost seem bubble like? A I able to reshape the sides a bit to make them straighter instead of round? Or can I not since they're already cemented in? I want to get composite veneers on my other teeth since they're pretty dark in person and a have a odd texture.