While i was trying to send my books to my Fire Tablet, i got an alert they were in the wrong format.

it offered to convert them. I did it but noticed i liked the other format better. i have an app that can read that format. I went to remove the AZW format. i can't figure out how to remove it in bulk. i don't want to have to through all 200+ books individually to remove it. When i click on edit in bulk, i don't see the option to remove/recycle.
All help will be appreciated!