You can remove a team member by going to Settings > Preferences > Click on your team name. There, you will see a list of your team members, and by clicking the three dots menu next to her name, you can select "Remove from team." Users are not notified when they are removed and can easily be invited back at a later time.
You do need to be an admin to be able to do this. If you are not an admin, the person who started your account should have admin privileges and can either do this for you or make you an admin as well.
There isn't a way to see which users are active vs. inactive in the app. If you need help determining which are active or inactive, message us at firstname.lastname@example.org and we can assist.
If you'd like to delete a team entirely, message us at email@example.com.