You can view all of your current leagues and switch between them by navigating to the "Your Leagues" page. Below are instructions on how to do so and a visual illustration:
1. From your dashboard, click the Side Menu Icon ("hamburger" icon)
2. With the side menu visible, click "View Other Leagues"
3. This will bring you to the "Your Leagues" page (it should have a dark blue background). From here, you can view your "Current & Future" or "Past" leagues