Where are extensions in Google Chrome and how can I remove one easily?

In the school district where I work there have been a few pop-ups and advertisements that have been coming up on teacher's computers. What appears to be the issue is that an extension was added. To remove the extension look to the right of your address bar and right click on one that you believe to be the issue.

The one that was causing issues was one entitled "Ads by PDF viewer".

Embedded below is a GIF followed by a 42 second YouTube tutorial.

Take care,
Brad