Currently you have to disable each user one at a time. Would be much quicker to perform this in bulk; ideally via .csv mapping.
The status for this idea was out of date. It is now possible to disable users in bulk. On the Account settings > Users page, select the users you need to disable and then set the User Enabled/Disabled option to Disabled.
This needs to happen to allow admins to easily clean up user lists that are populated throughout the tool as well as efficiently adhered to IT Audits