There is no "switching" of scholarships. You would simply turn down the AROTC scholarship this spring/summer and then join the NROTC Battalion as a College Program Marine option at the start of the fall semester at the university which you will be attending; obviously, the university has to have an NROTC Battalion for this to be possible. You would reapply for the Marine option NROTC scholarship starting in the fall, but if you earned it, it would not kick in until Day 1 sophomore year. So, bottom line, with this path you are paying for tuition your freshman year. If that is not a possibility for you, you may want to consider moving forward with AROTC. Again though, you can't morph your AROTC scholarship into an NROTC scholarship.