You may remove one or more folders after they were created. Simply navigate to the particular bucket and select the folder as well as click on 'Remove object' or click on the respective button next to the specific folder. This action also applies when deleting buckets. Note that the delete action is irreversible.
Navigate to 'buckets' and the specific bucket.
Select the respective folder and click on 'Remove object' or select the icon next it ...
... which also applies when deleting a bucket.