Redirect to WordPress directory

I have a site where my WordPress files are stored at http://www.atozenglish.jp/wordpress. I changed the server settings so that when people typed in http://www.atozenglish.jp it would automatically redirect them to http://www.atozenglish.jp/wordpress. However, when I did this, I started getting 404 errors. I called my provider, and they said I have to change something in my WordPress settings to make it work. Can anyone explain what I have to change, please? (BTW, I’m not talking about using .htaccess, I did this from my server settings panel).