And, if you don't have details listed foe user, here is the utility I created little while ago and it will help you to get users details quickly into report along with groups. Please try in your local first. It is compiled against AEM 6.1 SP2.
Please put up more details around the requirement. You want to delete the users from author? How many users you are expecting to delete and what details you have in your bulk users list. Did you sort out what users need to be deleted from AEM? To delete users in bulk you need to be careful enough.