Stuck on domain mapping from a sub-domain to an add-on domain

I created a sub-domain and got it just the way I want it. Now, I have a pre-existing url that I switched the nameservers to a different add-on domain as directed by the hosting service.
My problem is, everything is still on the sub-domain section, so I redirected the add-on to point to the sub-domain.
I need to somehow get the sub-domain files to show as the main site and url.
I know I probably way over-thought this, but FTP isn't an option. Help?