All teams need at least one admin - so make sure the team has someone else already in there as coach/manager. If that's the case then you are ready to resign.
The easiest way to achieve this is to ask the other coach/manager to remove you from the position. The alternative is to do it yourself. In which case;
This works both mobile, and on web.
1. Login as normal.
2. Find your profile
3. Look for the teams the profile is associated with
4. Find the team you are the coach / manager of.
5. And delete the team from your profile.
This actually takes you out of the team - not deleting the entire team. If you have kids in the team - they are still in the team, but you are no longer a coach or manager.