You can easily leave the team you signed up for, if you changed your mind.
Log into your account, and click on the settings button in the left upper corner.
Thereafter you pick "Leave Team". You will then be asked if you are sure that you want to leave the team. Here you answer "Yes".
You have now left your team.
If you want to know how to join another team, click here for help.
Do you want to create your own team? See this article for help.