The Army gives you several options of colleges to choose from when you first receive the scholarship offer. However, you have to choose to accept the scholarship at only one of them within 30 days. I assume you did that. You could contact Cadet Command and ask if it is still possible to transfer your acceptance to one of the other option schools you did not choose, but I don't believe you can request it at all if it wasn't on that original list.
I believe every college ROTC unit has a quota of how many scholarships can be awarded at their school per year. If the school you prefer has filled their quota already, you would not be able to switch your preference there either.
I would recommend you contact your point of contact at Cadet Command and the PMS of your other preferred school to answer your question.