Multisite - How to make a subsite the main site

I've styled a subsite using a different theme than the main site. I'd like to use the subsite as the main site. Is there an easy way to do this? Or perhaps copy the content and style of the subsite to the main site.
By the way, this subsite will also be the template for all the other Marktepress stores. New Blog Template works great for this.
Thanks!