You can access your subscription information and cancel your current plan on your settings page, which you can access by clicking your profile picture in the top right corner and then use the drop-down menu.
1. Click 'Settings' by in the drop-down by clicking your profile image in the top right corner.
2. Scroll down to 'Plan & Payment'
3. Click the text-link 'Cancel your subscription'
4. Select a reason for cancelling (Optional)
5. Hit 'Cancel subscription' and you're done.