You can either remove a Paid Sitemate User at a company wide level (e.g removing their access from all links), or just to a specific link in a folder.
Removing a Paid Sitemate User at the company level:
Go to the Home Folder
Select the Users tab at the top & click on Paid (under Sitemate Users)
Select the checkbox next to the relevant user & click Remove
Removing a Paid Sitemate User from a specific folder link:
Go to the relevant team folder (where the link was created)
Select the Users tab at the top & click on Paid (under Sitemate Users)
Click on Paid Users
Select the checkbox next to the relevant user & click Remove