If you need to deactivate a team member, click into your "Admin" button down to "Company Settings." Once you're here, click down on the lefthand side to "Team."
Find the team member you want to deactivate. Click the little pencil icon next to their name:
Once clicked into their profile, you'll be able to scroll down and hit "Deactivate User":
What this does will "freeze" their account. They will not be able to log in as long as their account is inactive.
Their name will drop beneath any active user and turn light grey on your Team list:
When you click into their name, you'll see "INACTIVE" next to their name. At any point, you are able to re-activate their account:
See more here: Reactivate a Client User's Profile