1. Login to your host and go to your SSL Certificate product page
2. Turn on AutoSSL for your website domain (top right select field)
3. Test that your website works with https:// in front of the domain
4. Check your website on this SSL Checker to see that the SSL is trusted, valid, and working properly

If you have a WordPress website, follow this step-by-step tutorial on updated your site from HTTP to HTTPS.

Checklist for Moving A WordPress Site to HTTPS

After you’re all set on HTTPS, follow this article to set your preferred domain in all of your SEO & Webmaster Tools.

How to set a preferred domain (with steps for WordPress)