Transfer subsite to primary site From example.com/redesign to example.com

Hello.

I have multisite project on WordPress and I would like to use a subsite as a main site.

I mean that I have main page on wordpress http://www.thoreo.com and I can’t edit URL path of this main site, I can not even delete it.

And I also have subsite http://www.thoreo.com/redesign.

My goal is to use http://www.thoreo.com/redesign as http://www.thoreo.com

Is there any smart way to transfer my subsite or I have to rewrite everything again?

Looking forward to see your replies and thanks in advance!

Peace,
– Lolek