Web
If you want to remove a team from your profile, you can do so from going to the "Danger Zone" on the player profile page and click on "Leave Team Forever".
Mobile
How to leave a team from the mobile app:
Tap to the "Account" tab
Tap "Teams"
Tap the team you want to leave
Scroll down to "Danger Zone" and tap on "Leave Team Forever"
Type in "LEAVE" and you'll be removed from the team and all seasons