Edit next/previous post

Currently, there is a menu at the bottom of each of my posts that I think is supposed to be “next post” and/or “previous post” and it’s set up to be the name of the blog post. I want to edit this to just say “Next Post” and “Previous Post” but have no experience of coding and wouldn’t know where to start without risking messing something else up.

I have been into the theme editor but couldn’t see the specific lines relating to this and don’t really want to install a plug in to do the same thing, as the code would still show what appears just now right?

Help appreciated!

The page I need help with: [log in to see the link]