You can remove members of your organization from the Workspace Members page if you're the Owner or an Admin.
Click on a member, or drag to select multiple members and remove them by clicking the “Remove” button up top:
When you remove a user from your organization, all the contents they created (projects, screens, sections, notes, and so on) remain.
☝️ Only those on the Organization plan will have a Workspace Members page. If you're on a different plan, you can learn how to remove project members here: Removing a user from a project