Double majoring in Engineering/Science

I am an OOS student and I was admitted early to the CHC at uMass Amherst with a very generous scholarship. I have indicated on my application that my choice of engineering is ECE. However, I might want to change it to Computer science later. Is there a way to change your major (and department) in uMass Amherst after say the first year?
Also, is it possible to double major in CS + ECE in four years? (I’m prepared to work very hard and take rigorous courses)