Engagement rings

If your boyfriend bought you an engagement ring and you didn't like it. Is it selfish to kindly say to him that it isn't your style, you love the thought and effort behind it, but it isn't your style? And would it Be okay if you went and chose one together? Nothing more, nothing less. More like it's the style of ring. Is it rude to change your ring because you don't like it? Not because you are ungrateful, but you have to wear this ring for the rest of your life and shouldn't you be in love with it? 

My best friends just got engaged and this is something that is happening to them right now. Please voice your opinions I'd love to hear them. Do you agree that you should be allowed to change the ring if you aren't happy with it, or disagree?