There are two ways how to delete a team or more teams at once.
At the end of each row of each team, you can find the three dots, and there is the option Delete. By pressing Delete you will delete your team permanently.
On the left, you will select each box of the teams you want to delete.
After selecting the teams you want to delete, you will go to 'Actions', and then press 'Delete.'
By pressing Delete, you will delete your selected teams permanently.