Selective Navigation Menus

pretty easy, just do something like…

if ( user_is_logged_in ) { do second menu }

Basically only showing the menu after they’ve logged in.

should be simple enough to accomplish.

Where do I put this code?

You’d put it in the header.php, wherever your navigation is.

We can’t specifically say where to look, as we don’t have access to commercial themes. We don’t know how they operate.
Your theme’s vendors do provide better support for your theme.