Once you have existing collaborators, you will see them listed below at Sidebar > Account > Collaborators.
The options on the right upper corner allow you to export the list, and sort it from latest to oldest, alphabetic order, and active or inactive.
You're able to decide on how many collaborators you want to be shown on the list and search for them on the searching bar.
On this list, you get the option to remove collaborators from your workspace by pressing the little trash bin icon on the right side of each collaborator.
Once you press the trash bin icon and confirm that you want to remove the collaborator, they will lose all privileges within your workspaces and be permanently deleted.