Zenkit

You can completely remove a member from your account and profile (this is especially helpful if someone has left your company and you can't remember which lists and folders they're a member of!).
To do this, click on your avatar in the lower left corner and then scroll down to the "Organization" section.

Then select "Manage Organization & Members." In the "Manage" section, you can now select "Users." Clicking on it will take you to a list of all members. Select the user you want to remove. 

Next, scroll to the bottom of the menu and select "Remove user from organizational resources". You will then be asked if you actually want to remove the user. Confirm this with "Remove".

Note: If the removed user is the owner of one of your lists or folders, you will receive an error message. Ask the person to be removed to transfer ownership to another team member.