Every member in Teams has a role, and each one has different permissions. If you want to make someone an owner or view who's an owner of an existing team, go to the Team name and click More options > Manage team. 

Owners

Team owners manage certain settings for the team. They add and remove members, add guests, change team settings, and handle administrative tasks. There can be multiple owners in a team.

Members

Members are the people in the team. They talk with other team members in conversations. They can view and usually upload and change files. They also do the usual sorts of collaboration that the team owners have permitted.

Guests

Guests are people from outside of your organization that a team owner invites, such as partners or consultants to join the team. Guests have fewer capabilities than team members or team owners, but there's still a lot they can do.