HELP. transfer development install to the root

I am developing a WordPress site for a site that is hosting the current site. I cannot install at the root in order to keep the current site up and running. My question is once I develop the new site at https://www.currentsite.com/dev – how do I transfer the WordPress site to the root (replacing the old site)?

Note: I used the “one-click” install provided by my host to create the current site.