Teams have two things to manage: team attributes and team membership. The team attributes are things related directly to the team, such as the description. Membership is the relationship of users to the team.
The attributes of a team can be edited by Space Admins in the Team's page. There will be an Edit Team button that will allow the Space Admin to update:
While membership can be updated within the edit team, there are also other ways to update the team membership. Anyone can request membership on a team from that team's page. This request will go to the Administrator team. Also, Space Admins can update a team membership by adding user's to the team from within the user profile.