@Kleo and @Robert have already mentioned the ways; I'll just explain them in a little more detail.
So, I get what you're trying to do. Now, there are two paths:
You might go the easy way to get started, however, I won't recommend this simply because a fully-blown CMS will be too much if you only want site-data changed.
The hard way, simply put, asks the user to enter the data, then stores it in a small database. Then you can very simply pull it out using some backend via REST, and display it with a frontend framework. :)