The user management system on Pathway will let you manage who has access to Pathway.
On Pathway on the left hand side menu you will need to click "User Management"
Note: You will need to have admin permissions for this to appear on the side menu.
Once you are in this screen you will have the option to to locate the user in question with the search box:
Once the user has been located you can click on the three vertical dots located to the far right under "actions":
This will open up a menu where you may select the disable button as needed: