If you are an Admin in MCA Suite, you can delete users from your system. 

To delete users:

1. Navigate to the Admin User screen

2. Search and select a user

3. Click 'Inactivate'

After this, you still have a chance to reactivate the user but they will not be able to login.

To completely remove the user from the system go back to Admin > User and click Purge All Inactive Users.