To delete a Role, click on the Red Trashcan icon to the right of the Role. 

This will open a message box asking if you are sure you would like to delete the Role. Click on Yes to delete the Role, or click on No to cancel the delete operation, and return to the Roles Overview. Be aware that deleting Roles can have a significant impact on the users of the system so make sure you check all the Users or Groups with this Role before deleting.