To have HTTPS, SSL Certificate is needed to be installed on the server. Another option is to use Free CloudFlare SSL
After activating ssl, edit the file
system/config.php and update the url, change http to https
All websites without a valid SSL certificate shows notification- "Not Secure", started from July 2018 with the release of Chrome 68. Moreover, you should always use business suite with HTTPS as it has login, authentications etc. & HTTPS protects the privacy and security of your users.