Before deleting users, log in to your WordPress dashboard.
In the sidebar go to Users.
To the left of each user is a checkbox. Check each user you want to remove, and click the “Bulk Actions” drop-down above the table.
In the drop-down select “Delete” then click “Apply”
On the next screen you will be asked to confirm deletions of this user, check all the details carefully and assign any existing posts/pages to a new user then click “Confirm Deletion”.