To update your web app URL, make sure you have the HTTPS certificate for the URL you wish to move to installed on your web server and available in IIS.

Configure a DNS record configured on your domain to direct traffic going to your new URL, to your web server.

Configure a HTTPS binding on your Halo site in IIS, selecting your covering certificate. 

Open the Config.exe application from the root of your Halo web app, and set the URLs to (your URL)/api/ for API URL, (your URL)/auth/ as AUTH URL, and (your URL) and Agent Web App URL:

Save this, then restart the Halo IIS site.

If you have issues navigating to the website after this, then go to this URL to clear your cache:

(Your URL)/API/instanceinfo?clear_cache=true