We had a custom theme designed for a new WordPress site we are building, so we set up the WordPress installation on our new server and installed the theme. However, it didn't work properly, so we got in touch with the theme designers.
They set up a new installation of WordPress on a different server, installed the theme, and got it working.
Now we want to transfer the "working" version of the site from the installation THEY set up to the installation WE set up.
What's the most appropriate way to go about this?