You can remove a member/user from a team in one of two ways.
1) From the Learner page, select "Team" and then click on the pencil (edit) icon to the right of the member's name. Uncheck the box to remove the member from the team.
2) From the Member page, select the member you wish to remove from a team. Click on the down arrow to the right of Learner. Click on the red X next to the learner's name to remove that member from the learners' team.