I uploaded CSV file to the CRM and changed the fields for first and last name without knowing the first and last name in my CSV file were incorrectly switched, so when I imported, all my first name field data was last names and vice versa. I deleted all of those names, but couldn't figure out how to delete everything, so now when I load the correct CSV file, the system isn't allowing me to change the first and last name fields to correct the problem =. Both of these fields are now greyed out and have a little hazard icon.