If you want to add or remove contacts from any of your teams - or if you want to amend the team name:
Find the team you would like to amend
Select the "edit" icon - it's the one which looks like a pad and pen
Edit the team name or add/remove your desired team members
If you no longer need a team and want to delete it, all you have to do is click the "X" icon to the right of the team name and confirm.