Why can I only see one season of a show?

On the right side of the Episodes section for a show, you should see a drop down box which lists different seasons for that show. Click the box to see the list of options appear. Select a different season from the list and any available videos for that season will appear in the videos below.

It's also possible the show you are looking at only has one season available for online streaming, but you can check the Seasons drop down box to confirm.