If you are the Team Owner, you will have access to delete a team.
From the app dashboard:
1. Press the downward arrow in the top left corner of the screen
2. Press the 'Manage Teams Icon' (icon has a screwdriver and a wrench on it)
3. Find the team you are looking to leave and press the delete icon (right hand side)
4. Press 'Delete Team'
From the Web:
1. Go to the Dashboard, click 'Add/Join'
2. Select 'Manage Teams'
3. Press 'Delete Team'