In a sphere (Admin profile)
Go to the profile of the member in question. Click on the "More" button, then select "Remove from this sphere"
Note: If the member does not belong to any spheres, they will still be a member of the organization, and will have access to the internal members portal.
Only a manager can definitively remove a member from an organization.
From the admin members page (Manager profile)
Select the profile of the member in question. Click the "Action" button and select "Remove this person from your organization".
Note: It is possible to perform this action simultaneously by selecting several members. In this case, you can use the button "For the X members selected".