You can remove a Portal user and take away their access in the Provider Portal by following the steps below:
Go to Administration then Security then Users in the Provider Portal.
Click on the user’s name to open the Edit User screen.
On the Details tab, find the Change Status box.
Click the Suspended button, the user won't be able to log in after that.
The status on the screen will update to Suspended once it's done.
Don’t forget to remove any roles assigned to the user if needed.