As an admin, or an owner of the team, you have the ability to remove a user from the team, for example, if a colleague left the company, go to Users in the left-hand menu.
There, click on the user you want to remove and then on the Revoke access button at the top right.
A popup will open in which you need to confirm you really want to revoke the user's access. If you're not sure, you can there still choose to cancel here. Otherwise, click the red button Revoke access to revoke the user's access to the team.