On Github

On the webpage you’ll see that your fork is behind what’s happening on the original branch:

Now click “Sync fork”.

Then click on “Update branch”. After a while your repo is updated.

Open Github Desktop

However, you still need to sync your local files. Here you have to “Fetch origin” in Github Desktop (or a similar app).

Now you’ll see this:

Then click “Pull origin”.

Then your local files will be updated, after a while.

Related video: Solve Merge Conflict