To change a team’s avatar, you must be an administrator.
Perform the following:
In the navigation pane, expand People and click Teams.
Click the team whose avatar you want to change.
In the upper-right corner, expand the menu.
Click Edit team.
In the Team avatar section, click Change.
Under Avatar, click Change.
Click Create Symbol and select an icon and color.
Or click Upload Picture, browse your computer for an image, and crop it.
When finished, click Save team.