How do I use a domain name with my raspberry hosted cloud?

I used the tutorial at http://www.instructables.com/id/Personal-Cloud-for-Self-organization/ to setup nextcloud on my Raspberry Pi 3 running Raspbian.

Everything works so far and I can access my cloud through the internet via the static ip address I configured.

I want to be able to access my cloud using a .com domain I just registered but I don’t know how to do this.