Currently, the way to de-activate a user is to do so manually by going to the People tab, select the user, then click the big red 'Deactivate' button in the top right. This will mean the person can no longer log in, but their reporting information will still be available in the reports area should you filter on Inactive people. It also means that the user's profile will automatically re-activate should the user purchase a subsequent course from your organization through the eCommerce page, using the same login information.
Deactivating Users in Bulk
To deactivate users in bulk, go to the People Tab and choose "Select All" located underneath the search bar. Once you have selected this option, look for the white drop down on the right hand side of the page and choose "Deactivate Users". You also have the ability to "Reactivate Users" in bulk now, too!