If you mean "big" by "major", you might say: - 저의 큰 꿈은 시각 정보 디자인입니다. - 저의 야무진 꿈은 시각 정보 디자인을 하는 겁니다. * 시각 정보 디자인 = Visual Communication Design. Communication is exchanging information (정보), so 정보 디자인 is equivalent to "communication design". Some universities have departments named 시각정보디자인과. * 야무진 is not exactly "big" or "major", but it can be more interesting to say (in informal situation). It's similar to "ambitious" (원대한) but in the slightly different sense that you value something very much and will stick to it to the end giving your best efforts.

Well, I'm actually not sure what the English means, but I'm guessing you mean something like: It's my dream to major in visual communication design. If so, you could say: 제 꿈은 비주얼 커뮤니케이션 디자인을 전공하는 것입니다. or 저는 비주얼 커뮤니케이션 디자인을 전공하려고 합니다. "I'm planning to major in visual communication design."