Follow these instructions to delete a team. N.B. It is not possible to reverse this action once you have clicked "Delete team" in step 2. All team content will be deleted. This should not be done without careful consideration.
1) Open Teams and next to the team's name click on the three dots and select "Delete the team":
2) Read the text cearfully: "Are you sure you want to delete the team? All channels, chats, files and the Office 365 Group for this team will be deleted." If you are sure you want to delete the team click the checkmark "I understand that everything will be deleted" and then click "Delete team":