I contacted them by phone at the placement extension. My son faxed a request to change schools before he received the original paperwork. I called to confirm the next day that the fax was received, and the lieutenant who answered the (placement) phone said that she had already processed it.
My son then completed the original acceptance paperwork and faxed it in. He followed with the captain at the school he transferred to, but it took probably 3-4 days for the captain's paperwork to show that the transfer had been completed and then another 2-3 days to show that he'd accepted the scholarship.
His paperwork took nearly a month to arrive, even though the website said it should be delivered within two weeks. The NROTC captain asked for our patience, saying that there were several thousand scholarships awarded and a small staff to handle the paperwork.
My personal opinion is that the phone and fax route is the fastest way. Good luck!