You can't delete organizations from PLIC Books or PLIC Elements. You will have to go over to plic.io. After you login, go to My Organizations from the left tabs. From there, click on Sub Organizations.

Find the school that you want to delete and click on the name in blue.

Once on the school that you want to delete, verify the name at the top matches the name of the school you wanted to delete. Next, click Delete Organization. Please note that this will also delete all projects and users under this organization, and cannot be undone.